just bought a 1988 iroc z convertable that originally had a 305tbi in it. This was replaced with a 350 crate motor that he bought off ebay with claims of 310 hp. While i find this hard to believe, how can i check if anything was done to the original tbi as im sure it wouldnt deliver enough fuel. The car certainly hasnt got no where near that sort of horsepower!!!! What else should i check for?

 

Crate motor could mean a "short block" or a "long block". If he got a short block and transfered the heads and TBI it would probably not be 310 hp.
Get the casting or part numbers off the heads. And/or take it to a dyno and find out what it is actually putting out.

 

310 horsepower with a carb on it does not equal 310 horsepower with a TBI unit on it.

Along with the head casting numbers as said above, you can get the part numbers off the fuel injectors to see what size they are.