As odd as it sounds, engine mounts are now one of the items that are better being sourced through the junkyard over new pieces from any parts store. Even though you don’t want to get them from the junkyard you would be so much better off by doing so as NOBODY sells engine mounts that are worth a hoot these days. Not even Napa and GM has discontinued them. Apparently all of the Part Houses (Napa, Vhatozone, LMC, etc.) are purchasing mounts from the same Taiwanese supplier. They are all horribly paper thin junk! I would just get your hands on OEM mounts from a junkyard and if the rubber portion is toast just add the Energy Suspension engine mount inserts.
Here is a related thread on the engine mount topic from last year. My truck ate two sets of Napa mounts before I gave up and found a set of OEM mounts from the junkyard then added the Energy inserts. Problems solved!
Good move on using the later mounts in an older truck. I did the same to my ’72 but only changed the towers instead of the entire crossmember.
The engine mounts (and TBI engine) I used were pirated from a 1990 Gvan.