I have owned GTO's since a was 17 (I'm 37 now). I do know a bit about them. I have a 1966 GTO right now it has a 400 4BBL in it right now mated with a TH400.
I have a 1966 tripower unit that a friend gave to me when he took it off his 1969 Judge( a long but funny story here is the short version-"My friend bought the 1969 Judge from a farmer who was the orginal owner. The farmer didn't like how the RAM pans looked on the car and replaced the set up with a tripower unit. My friend pounced on the car when it was for sale. In the trunk of the car was the orginal carb, manifold, and the ram pans. LUCKY ME I get the tripower unit for my 1966gto that's what friend are for").
Sorry for the story but it was a good one. The real question I purchased a 455 that was pulled from a 1973 Grand Am. It has 4X heads and is pretty complete. It was frozen but, after the tear down I found that the block and the heads were in good shape. I want to keep the block,the heads, and the crank( also in good shape). I want to install the tripower unit and put it in the 66 GTO( I know i've got to change the motor mounts which I already have).
I have seen a 455 tripower engine before but I am at a loss as to where I can find some specs over one.
Is there anything super special that needs to be done to the internals of the engine when building it. I'm looking for between 400 to 500 horsepower when everything is said and done. I know 4X heads are okay when some "work" is done to them. Any advise please.