I'm no expert on port size differences between the 248/270/302, so this might be irrelevant without some sort of step down rings....
But here's a GMC 302 - 2 barrel manifold on EBay. Seems like a reasonably fair price, too. (Not mine)
https://www.ebay.com/itm/122015849536 Might open up some different carb options as long as you stay CFM matched.