The block sounds like an over the counter replacement 350. I seem to recall running across the MA designation before. If it was an OE engine installed in a GM vehicle, the assembly stamp would be Vxxxxyy(y) or something similar, and there would be a partial VIN either on the pad or on the flange above the oil filter.
A check of the block date code should confirm it is not a 68 327, and the casting number off the crank would confirm. The bore is the same.
69 'vert project big block/TKO 600 RR
68 'vert driver RS clone -- gone!