David, remember in kindergarten when you had that board with the round and square holes in it and you tried to put a square peg into a round hole? It didn't work. But you could put the round peg into the square hole, right? Same thing with your manifold, it's a square peg and you're matching it up with a round (oval really) hole. It's a big block chevy, so it's gonna run pretty well regardless of the mismatch of parts, but you'll never know how well it might have run with matched-up parts. The mismatch at the manifold/head port interface will generate turbulence, but again, it'll run o.k.