I've got a '66 425 with B heads i plan to use in my '67 Cutlass. I have a '69 455 with C head also, but i'm going to use the 425 b/c of the internals. Since i have both sets of heads, i was wondering if there was a performance or flow difference. I know I'd have to enlarge the pushrod holes on the C b/c of the *45 cam bank, but that wouln't be really necessary if they are the same performace wise. Both came out of 88's from each year. Opinions?

 

If it were me I would use the B. Being they both need to be rebuilt,The C will not flow that much better than the B. Then you can sell the C if you want, and they will be easier to sell than the B heads.

 

Use all the guts from the 425 in the 455 block. That way you can get any cam real easy. "B" heads "C" heads not a noticeable difference. Do port work and you will be better off.
take .020 off the block and .020 off the heads and that makes up for the fel-pro .040 head gasket.
Gene

 

Use either pair.No difference.

 

Good tip above on using the later block. The 66 425 uses the old 45 degree ifter angle and needs a specially ground camshaft. The 455 F block uses the common 39 degree and you can use off-the-shelf cams. you can put 425 piston and rods into a 455 block, but would have to grind reliefs in the 425 block to put 455 stuff in it.