A 530 head has a chamber of 48cc, the last four 531 heads I've rebuilt have a combustion chamber size of 52~cc depending on what was shaved off. I've literally just cc'd two 530 heads I have, and one has had work done, and is 47.5cc, the other is dead stock never been off before and it's at 48cc. The last 531 one I rebuilt was at 51.5cc.
The piston dish in a b230ft piston from a 1988 block is 16.0cc, a stock elring head gasket squish is 0.47' which is ~1.2mm, so given the 80x96 stroke to bore sizing, the compression calculator comes up with 8.5 with 51.5 cc and 8.8 with 48cc of the 530 head.
Further, I've measured a 94 b230f piston I have spare and that is at 6cc dish. Which with a 530 gives you 10.0 c.r or 9.6 c.r.
Pictures added as the source, it's my own burette and the link to the calculator is here
http://www.csgnetwork.com/compcalc.html
Variations are usually in the piston deck height, I may have the head gasket diameter wrong by 0.5 smaller than I've now measured but that is negligible for compression.
My previous measurements to come up with 0.3 were from measuring another 530 and 531 at the time also. So age variations with machined once heads will alter overall values. But I'd say the average is closer to 0.4 cc difference but with power gain from flow and better plug angle.
