Having done some basic calcs, as I've been thinking about head skimming on my 109, for 7:1, the total clearance volume should be 95.2 cc, and for 8:1, 81.6cc.
The total clearance volume should include any clearance between the top of the piston and the deck of the block at TDC, and the volume enclosed by the clamped cylinder head gasket.
I can believe that to go from a 7:1 head to an 8:1 compression ratio would need about 100 thou taking off (this implies the bath tub takes about 83% of the bore area), but, I struggle to believe the quoted figure;
http://www.expeditionlandrover.info/landRoverFAQ/FAQ_head.htm
of only 20 thou to go from 8:1 to 9:1 - I make it more like 75 thou, assuming the same shape, i.e., 83% factor.