Kerry, 1937 was the first year Buick used the prefix digit on the engine block to denote the car series. It makes sense the first digit is something other than 4, 6, 8, or 9 on a NOS block which has never been installed.
For 1937 it would either be a 248 or 320 cid. The cylinder bore and main bearing dimensions are larger on the 320. The attached pages from the shop manual show the differences.
The 1941 master parts book shows the cylinder crankcase (group 0.033) came with pistons, pins, and rings. The part numbers are shown on the attached page on the slim chance there is a tag or some marks indicating the part no of the block.