If you're wanting a stock-ish 4150 flange you might also look at the GM 359 intake that all the S/S L78/L72 guys are running...there's a little bit of extra HP there out of the box, and you'd be starting with a nice, new part. Also, if you're stuck on the original ZL1 block I'd at least Ebay the 074s and buy a set of oval port Race Rites or AFRs (or another aluminum head of your choice)...the newer heads will ease your mind in regards to pulling studs/guides/dropping seats and whatever else plagues those old aluminum heads, and you'll be ahead of the game performance-wise. And, an iron headed bbc/400thm combo can get down to 3500lbs pretty easily [minus driver] so the aluminum engine is gonna chop another 150lbs or so off the nose [where it's most important]...you'll add a little bit back with a bigger bottom end, but not enough to sweat it.
You're biggest challenge is gonna be getting it off the line...ask me how I know...
