The holes in a triangular pattern on each side may be for side mounted motor mounts.
Don't think the hole above the oil line with the green arrow is threaded, should be the oil flow pin. When driven in it's for the full flow oil filter. If pin is flush it's setup for bypass oil filter only If pin is driven in it must have external oil lines!
BC 1960 Chevy C10 driver 235 T5 3.73 dana 44 1949 GMC 250 project in waiting 1960 C60 pasture art G.M dealer tech since 1980 & counting