will the 4.3 v8 heads bolt on to the 5.7 v8 or are the heads a diffrent size i no the intake manifolds are the same im not sure

The L99 heads have smaller valves and chambers.

I would not bolt them on though they will "fit".

Here they are side by side.

http://i120.photobucket.com/albums/o165/96capriceMGR/DCP_0315.jpg