TOPIC:

Looking for info specific to the 81 twin plug head with integral injection port.. valve sizes, chamber volume, etc.

I reckon you will have to either ask the guy who made it, or take those measurements yourself.

Chamber volume for the stock  B1 injection head is 40cc ( as it is for all 1000J and GPZ1100 heads ) and your head appears to be unskimmed by any significant amount if at all as the lip around the combustion chamber is still intact.
Stock steel valve size would be 31mm inlet , 37mm exhaust.
Current stainless ones may be stock size or oversize.
Also as mentioned elsewhere on FB the B1 is single plug as stock (as are all kz/gpz heads ) and the extra vertical 10mm plug is a modification..