Bore of 4.00 x 3.50 stroke will be a 352

Bore of 4.05 x 3.50 stroke will be a 360

Bore of 4.05 x 3.78 stroke will be a 390

If they did a .030 overbore on the rebuild you can bump up those numbers to 4.03 and 4.08 respectively.

I have seen 68 half tons with both 352's and 360's from the factory. I guess it depends if it's an early or late production for that year.