273 according to the hot rod article it looks like a set of hogged out and port matched 318 A body exhaust manifolds would work just fine. The HP and torque on stocker 318 manifolds for the same given RPM isnt much less than the 340 HPs. Headers honestly for the most part suck for street applications IMHO.
Yes my A body 318 manifolds are very close port size to my 360 heads and have a 2" outside to the exsaust pipe.This is only going to be a street cruiser,but still want a little snap from time to time.