64 was the last year that 389 had fairly thick castings, in 65, and 66 Pontiac cast a lot of 389s with thin cylinder walls, so you picked the right year to save.
Back in the early 70s I bought a 65 GTO that had a ton of machine work done to it. It was .060 over. The first week I owned it the cylinder wall collapsed, and the piston ended up in the water jacket. I had the clutch in, and revved the engine, and then it stalled. Not aware of what happened, I popped the clutch to restart it. The crank broke in 5 separate pieces, and it just broke everything inside of the engine. I was able to salvage 4 pistons, the cam, and lifters, cylinder heads, and the intake manifold. Even the timing cover got cracked when the crank broke. It happened at about 3000 RPM. The damage all ensued when I popped the clutch with the piston cocked in the cylinder after the cylinder wall collapsed, initially stalling the engine.
Right after the carnage happened I was reading in one of my magazines that 65, and 66 had thin cylinder walls, and the maximum bore should be kept to .030 over.......
A few days late, and lots of dollars short.....
I paid a lot of money for that car mostly because he had all the receipts to document the work, and the parts in the engine. I wish I had read the magazine before I laid out all that money......
