Hey everyone,

I am buying a 73 Riviera tomorrow morning after unsuccessfully trying to find a mechanic in California willing to swap my 83 Monte Carlo's 305 for a 350. It has the big block 455, but the 73 has a dramatically reduced HP (down to the low/mid 200s I believe) and lower compression than the stage 1 455s that were originally used by Buick.

What are the main changes that caused that result specifically in the engine? In other words, what do I need to replace in the 73s 455 to get it closer to the 350+hp that the 455 originally had?