will 73 big block heads 990's fit on a 1990 454 SS truck motor?

 

Yesir

 

your 100% sure right.

 

Yup, only thing is the early heads didn't have hardened valve seats, for unleaded gas

 

thanks

 

A set of L29 Vortec heads (oval port) would flow much better. I see them available sometimes in auctions or on Craigslist.

 

They will bolt on and work, but I seem to remember the 990's being a rectangle port intake design. The 1990 SS heads are the round 'peanut port' design. You will have to come up with the right intake!!

 

The 1990 Big Block is a Gen-V block and has parallel coolant flow instead of series flow like the Mark-IV blocks. It would probably be wise to research this somewhat before doing this, I don't think the Gen-V BBC has enough coolant passage in the back for series flow.

 

What year did the General start using hardened seats?