having trouble identifying inline 6

[cell]

Quoting from my "Catalog of Chevy Truck ID Numbers 1946-1972":

"The 6-cylinder engine unit number is located on the pad at the right hand side of the cylinder block at the rear of the distributor."

Hmm, mine doesn't seem to have a number there.

I do have the following numbers on my engine block:

passenger side, to rear of dipstick: CON 2
passender side, in front of dipstick: K156
passenger side, to rear of fuel pump: 3851659
below that: GM (in large letters)
below that: 7

driver side, in front of midline just below the head: 11
driver side, to rear of midline just below the head: 1659

My bore is definitely 3 7/8 inches, which is normal.

My stroke, however, appears to be 4 1/8 inches, which is neither the 250 nor the 292 (it would be something like 267). Perhaps I am measuring this wrong? I rotate the harmonic balancer, note the the pistons come up flush with the top of the block at top dead center, then rotate until one of them appears to be at bottom dead center, and measure from the top of the piston to the top of the block. Is this the correct way to measure this?