Can you put 2000 Chevy 350 Vortec heads on a 1995 block and increase horsepower with out modifications?
It is not possible to upgrade heads on a 350 block without needing to make any other modifications. The 1995 350 uses the older-style "Vortec" heads, that are less efficient compared to the 2000 350 "Vortec" heads. To realize any horsepower improvement from just swapping the heads, you would also need to make additional modifications such as upgrading the intake manifold, throttle body, fuel injectors, and possibly the ignition system to get the most of the upgraded heads.