From my research the reinforcement webs were only used on '73 and '74 truck engines. The four bolt motor mount also indicates it is a truck engine or FT engine. If the date code is 8M13 that would be December 13, 1978 which doesn't seem right. It's more than likely 3M13 which would be December 13, 1973. It could be a 330, 361 or 391. There's no way to tell without measuring the stroke. The 352 stamping is normal.