[Sportyworty]

The casting dates on the block and heads (under the valve covers) will be the answer. There will be one on the intake possibly but some marine manifolds did not. That timing cover is marine specific as well and also interchanges. Yes all of the Windsor family valve covers interchange. The 351 has its own intake and oil pan. There is also a stamped engine assembly date on the block to the right side of the timing cover. It is located on a pad just below the head. Many of these H/M boat engines were just garden variety engines. Some were solid lifter hipo 289's with Paxton blowers. I have bought a few Granatelli versions and the Paxton Gauges were worth more than the boat and the engine if not a solid lifter. Hipo. A pre 66 engine will also have a five bolt Bell as opposed to a six.

221 3.50x2.87 offered in 62
260 3.80x2.87 late 62-64
289 4.00x2.87 late 63-mid 68
302 4.00x3.00 mid 68-93