here is a pic of the current fresh 454 flat tappet I have. I have yet to bolt everything up to it. Any idea how i can tell what the hp is on this ? After I get this in the water this spring, is there a calculation with rpm- speed and prop type that will tell me.

Thats pretty funny that you posted an engine with LS6 valve covers. A Merc 420 is basically an LS6 with with different cam, compression and roller rockers.

http://www.offshoreonly.com/forums/g...-hp-specs.html

I have a 1970 chevelle ss with an LS6. My wife got me thoes in case I wanted to put them on but they look strange to me I like the stock ones. I am pretty sure the heads are closed chambered and rec ports on an ls6.

here is a block i am looking at using. It is complete. let me know what you think.

3999289 2 bolt main block
353049 large oval port heads