(umm... Mods? When does the snow storm end? While it's a nice change of pace from the usual, it's a little distracting when I'm writing this post... )
Well, first... I don't / haven't owned an 8.1. If you can't get past that, maybe stop here...
A little while back, I debated (internally) about getting my hands on an 8.1, to replace the 6.0 in my truck, because of the torque potential. I eventually decided... 'against'.
I'll share what pulling 6000 lbs of travel trailer is like with a LWB 5.3 Envoy... you feel it, to the point where you're bumping up the assist on the trailer brake controller. I used it to pull my current trailer from PA > IL a couple of years ago, and even though the Voy was mechanically sound, with all of the maintenance / repairs I had performed on it before starting towing with it, I decided after that trip that it would not be towing that trailer.
Did I get into an accident, or kill anyone? No.
Was I over the rated towing weight? No. Even had another 1200-1800 lb in reserve, per GM's 2003 rating (which governed).
Was I conscious of what I had behind me? Oh, yes.
Did my underroos have skid marks? Not saying, but I did hop in the shower when I got home.
Now, a boat is a bit more streamlined than the average travel trailer of that weight range. So it's not like 'pulling a sail'. But -- at that weight and above, I think one is better (and safer) stepping up in capability.
Most people with 6000lb boats aren't towing cross-country, however, so your trips will likely be shorter than mine. But you still have to deal with launch / retrieve. I have no experience with that, but I know I wouldn't want to be embarrassed at a boat launch, if I couldn't pull my own boat out of the water. Or hurt someone / myself, pulling the thing around.
So... I'm voting for the larger platform, which besides larger brakes, heavier frame, etc., also has switchable 'tow mode' which makes use of a second set of shift logic tables for the transmission (and if you go for a 3/4-ton platform, you'll get a heavier-duty trans, as well).
Moving on from platform sizing, we'll talk engine.
The 8.1 is a bit of a 'hybrid'. It's basically a Chevy big block, with the distributor and carburation replaced by LS-style engine controls.
It's a heavy engine, because the heads as well as the block are iron.
The heads, while having canted valves for improved airflow, aren't backward compatible with the old 396 / 402 heads, as the bolt pattern and number are different (so, no direct head swap). GM never made an aluminum set for the 8.1, although at least one aftermarket set exists (and they ain't cheap).
Why do I fixate on aluminum heads? Besides the weight, aluminum also dissipates heat better than iron, and that's especially beneficial in the cylinder head. If I have a choice between an iron and aluminum head, I'm going to almost always side with the latter.
Pros:
- It's a torque monster. The engine develops more at 800rpm (in stock trim) than any stock LS engine. (this is what I was thinking.... 'torque torque torque'). The cylinder heads are a bit part of that, with their canted valves (big airflow).
- GM strengthened the block a bit, and changed to 4-bolt main caps on all 5 bearings (many 'Rat' motors had 4-bolt mains, but only on the inner three bearings).
- You get bragging rights and the claim of something 'rare', if that's important to you.
- If you want to modify it, you can do so. Mild to wild.
- Low compression makes it a great candidate for boost method of choice, if you want it.
- It's not diesel (so no having to learn that architecture / maintenance / repair regimen, if you're not buying 'new').
Downsides:
- Being based on the old big block architecture (which was based on the small block), it's not as robust as the LS. Take the mains, since we mentioned those, above. All LS engines have 6-bolt mains (even the 'lowly' little 4.8). That's just one example. In short, the powertrain engineers started with something very good (SBC), and after they were done, had addressed all of the limitations of that engine, with the LS. 'Very good' became 'great', to the point that 'LS swap the world' isn't just a meme.
- Fuel economy is worse in the 8.1 (and the big block ancestors) than with the LS. Even the thirsty 6.0 does better, both unloaded / loaded. The less you drive, the less this is a factor, but... 'times are a changin'. And they're changing quicker than I imagined, at least. E.g.; what will fuel availability, emissions regulations, etc., be in 10yrs? Longer?
- Aftermarket support, while good, isn't close to what's available for the LS. Cam choices are somewhat limited (stock is around 330 whp and 450 tq, iirc) I'm in that ballpark after doing a cam swap in my 6.0, and there's more to be (safely) had.
- (as far as I'm concerned) You can build more power, with better reliability and fuel economy, cheaper with an LS.
There are other things I haven't mentioned, both 'for / against', but you get the point.
Now... that being said... it could be an
excellent project motor, if that's what interests you. It will take some time, a fair bit of coin, and a lot of effort... but you can build something really robust, if that interests you. If I were to get one, it would be with this in mind; keeping one stock (but just catching it up on 200K mi of maintenance) would just be kind of a wasted opportunity, IMHO. In short, you're building it *because* it's such a rare bird.
Bottom line: If you're just looking for the 'best available tool' to pull your boat, and want a minimum of headache... get a 3/4 or 1 ton SRW with the 6.0 (or 6.2, if more recent), and don't worry further. You can always upgrade it later, if you decide you want more.
If the idea of having a real Big Block engine just makes your heart go a-flutter (and one that's not super-rare, like from the 60s, so modifying it won't ruin its intrinsic / collectible status)... then
nothing else is going to do.
Since I drive a lot farther, I voted for reliability & fuel economy (marginal tho it may be). If I were doing sub-200 mile jaunts with a boat, on a seasonal basis -- I might go the other way and put an 8.1 under my hood, since I'd have a big off-season to plan mods for (here where I live in IL, boating is
very popular, but boats spend 4-5 months in the water, at most)
Hope the above provides some insight, when making your choice. 🤷♂️