My heads have leaky valve guides and does not have harden seats. I have a fresh set of 350 truck heads and was thinking about putting them on my 400 block. What do I have to change ? ie: what Head gasket do I use a 350 or a 400? What about the stem holes? The 400 heads are out of a 1970's car and the 350 heads are out of a early style 350 ( larger holes for the assories) truck. I know i will have to drill out my brackets but mostly don't know what gasket to use. Any help or insite would be great

Rick

You will need to use the 400 gasket, and drill the steam holes(you can use the gasket as a template). The performance characteristics or the engine may change. The 400s typically used a larger cc head then the 350. You will most likely see an increase in compresion.