Your engine started out with a 3 3/8 bore and a 4 1/16 stroke. If it has not been rebored already, an .030 overbore would be appropriate but generally a machine shop will not (should not) rebore until they have the new pistons on hand. For many years now, 3 3/8 oversize pistons have been hard to get, partly because the preferred solution was and is to bore to 3 7/16 which is 3 3/8 +,060 but also the standard bore for Chrysler and Desoto as well as later Dodge trucks and Industrial 251s and 265s. This has been my choice and in 50 years I have discovered that of all the bore and stroke combinations, 3 7/16 (3 3/8 +,060) by 4 1/16 produces the sweetest running engine.
Few Americans have had any experience with Canadian 3 3/8 engines.... the 218 and the 228. When ordering parts specify a 251 and you will not go wrong for gaskets,seals, valves, chain water distribution tube oil pump and distributor. You can even use the newer head gasket with the bump on front.
You may PM me if you need more information.