Sorry, that was supposed to read "spread bore". Square bore has 4 bores all the same size, spread bore has small primary bores and large secondary bores. There are at least 2 Chevy manifolds on Craigslist, one is a factory low rise aluminum spread bore, looks to be from the mid to late 70's $60. The other one is overpriced factory cast iron spread bore, late sixties - early 70's $100. Also, if you look, there is an Edelbrock Air Gap RPM-good price but not what you want.
