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Dave have you tried Imperial Services or Schumacher? They have all kinds of oddball mopar mounts. Mainly car stuff, but they may be able to help.
how are they different from a 4x4 Dodge of the same era?
After about 5 minutes of poking around 0n eBay - $42 delivered. Same as the 383 PU mounts apparently...
One of the main points of confusion is caused by a design change in later 318LA series engines, where one mount is staggered compared to symmetrical Poly mounts. There [LA] you can actually use the right side LA mount on both sides, but reversed when used on driver's side.
Otherwise as Aaron mentioned, no difference to speak of. If your front mounts are beat to poo you might want to carefully inspect the rears at bellhousing support crossmember. These tend to separate. Carefully jack tranny just a wee bit, only enough to lift it maybe 1" or so [because they do want to separate], and see if the mounts simply expand upward or instead want to split off the metal mounting plate.
Separated rear mounts aren't such a big deal but they tend to force premature wear on front mounts as engine/trans jacks around under torque effects.
At least up until recently Anchor was still producing both, or actually all 3, styles of mounts but I don't have the numbers.