If your heads are the original ones on your Bird, they were the most desireable heads in '55, have the same valve sizes as the Cs, and about 8.5 compression.  With a little port work and maybe bigger exhaust valves, they would be equal to the Cs with the same modifications.  Unless you are going racing, the G and 113 heads would not make a difference you could feel in the seat of your pants.  But you can feel it in your mind.  You could mill either the Bird or the Cs about .035 to keep the compression up with the composition head gaskets of today.

I have a pair of Gs, I think I have a pair of Cs, both would need complete rebuilds, that I would sell.  Shipping on heads runs about $40 per head, money you could spend on your present heads.  I'm not trying to talk you out of (or in to) buying different heads, I just think for street use your heads are very adequate.

John

If we are going to continue this discussion, we should probably switch to the Technical section.  But, although the Blue Thunder is definitely the best Y manifold for performance, for your use the 3-2s would probably work fine.  Personally, the "wow" factor of the triples is greater than the Blue Thunder.

John