i have a 93 z28 camaro.
was wondering if upgrading to Lt4 heads would be the best way to go?

 

To accomplish what? Porting the stock LT1 heads, with the correct camshaft and supporting mods will take you towards 500 flywheel HP. If you want to push it over that, the LT4's or some aftermarket heads will help you get the required flow, with some really good port work.

If you are simply replacing the STOCK LT1 heads with STOCK LT4 heads, it is not cost effective. You may see 15-20% flow increase with the LT4's, but you would see a lot more flow using the same amount of money to work your LT1 heads.

 

i was going to tell you the exact same thing as above. The stock lt1 lt4 difference isnt worth the cost. They become useful in high hp motors because they have more potential. Look into LE and AI for porting stock lt1 castings, one of the two of them would be my advice. And you ll find plenty of guys on this board will tell you the same.
Search around and look at the results, you ll find what your looking for. Remember to think of all the suppporting mods a 375-425rwhp car is going to need though. There are lots. good luck