@5tjss , head R&R on these is a total bitch. Broken head bolts, access to timing components, the cost of rebuilding the head. Might as well just throw in a good used engine. Some have done it successfully after swearing it off forever. The broken head bolts is the worst part and it ALWAYS the rear more difficult ones.
Mooseman, I have been researching this for the last 6 months, and I have yet to come across anyone who has dealt with it, who had an opinion different from everything you just said. I've got the GM dealership shop manuals, and it's only my aversion to spending money that has kept the idea alive after going through those pages. It's like nothing else that has been produced, all traditional wisdom about heads, gaskets, etc goes out the window. Not many places to turn for experience backed guidance if it gets hairy (and you know damn well it will get hairy) because most folks had enough sense to walk away from it.
Local shops want around 3 grand, a rebuilt crate engine, ready to install, crate delivered in my driveway, is the same price. I've had difficulty finding a used engine because every one that's been junked have died of the same issue. Overheated and eventually became undriveable and too costly to repair, so Pull-A-Part got some more Envoy's. Every single one. Clearly that's a design flaw. I'm thinking the hardware isn't durable enough for the forces produced at times, and starts failing and it cascades into other components. Flimsy thin parts, and that's what happens when they start letting the marketing department have a say in the design work over in the engineering department. I had a 1970 Nova when I was 16, paid $200 for it. Straight six, got real hot one day and cracked the block, but i drove it 2 more years and the all-steel radiator never blinked. I could stand inside the engine compartment while working on it. I like this truck and it has a great history and story to tell, I love what the unusual design can do at certain times for performance, but I need some tougher components. This chinese paper-aluminum crap is out. And whoever it was over at GM, who thought making plastic radiators was a good idea, needs their butt whipped out in the street for that.
Any info on heavy-duty rebuilds? or component suppliers? General guidance on what a guy should do with a truck in this condition? I'll bail and go find a 1970 Nova if the general consensus is to get out while you can. A 4-door granny Nova is still findable, nobody looks cool in those. Except me. 💩