IIRC the 848's nominal compression is 8.25:1 on the 235, with a combustion chamber volume of 5.414 cubic inches (88.7cc).
A 261 with the 848 (assuming nominal chamber volume, which is seldom accurate) may be as high as 9.0:1.
I assume a volume error for most heads at 3-5cc, depending on the shape. A large area cast chamber like the stovebolt will favor 5cc, so the 88.7 may be closer to 94cc and yield 8.6:1 - but still a substantial increase.
