Well to accurately answer this question it would be helpful to know a bit more about the engine, and the vehicle it is intended for. A couple bits of information that would help in the selection would be:
-Cam profile (lift, duration, LSA)
-Car and the cars purpose
-rear gears, tranny, and stall
-Future possible modifications.
That would help narrow it down a bit. That said, for aftermarket heads, Id be looking at Dart, Trickflow, and AFR heads. I have heard great things about Dart and AFR and have personally used trickflow heads. A general starting area for head size would be 175-195CC intake runners. That will depend on your camshaft profile. If you intend to keep the Performer intake and 600cfm carb and go with a cam that fits those, Id be looking at the smaller side of runner sizes for the heads to keep your air velocity high.
I hope this gives you at least a general idea.
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