What are the casting numbers of the heads? If they're the small oval port heads (aka "peanut port"), they suck for anything much over 4000 RPM unless ported and valved. Not even worth the work, IMO. AFAIK
, no intakes were made just for them either, except OEM Q-Jet cast iron.
Supposedly Weiand makes one "peanut port" manifold, the #8017 Action Plus. Has a spread bore flange. Whether or not it's actually a PP intake or one like the Eddy Performer 2-O, I'm not sure.