The "352" cast on the front of the block was common to all FE's from the mid 1960's until the end of production in 1975. It's most likely a D2 block if it's original to the truck, making it either a 360 or 390. These will both have the same bore, but different reciprocating assemblies.

If the heads are off, measure the bore and stroke.

4.05 bore x 3.50 stroke = 360
4.05 bore x 3.75 stroke = 390
4.13 bore x 3.98 stroke = 428

As far as I know, the 428 was never sold in light trucks. Typically you would get a 352 in the early/mid 60's, 360's and 390's from 1967-1975.