Is a 383 top end kit compatible with a 400?

 

Yes but you need to pay attention to compression ratio and cam duration. The 400 is a very low compression ratio engine (8.0) so head cc makes a difference. Cams with more duration will lower the dynamic compression ratio, so it might be a situation where are you mill brand new heads a few thousands.
Compression and timing is the key for getting the BBM to run, I run 9.5 with iron heads and premium unleaded aluminum heads can generally go a full point higher. It’s fairly easy to make 500hp with iron heads.

 

Thank you