Motor mounts for 351 V6 in C2500

[gophersnake]

The stock motor mounts on this truck are pretty inadequate. They start out as tidy rectangular blocks of rubber but after 10 years or so they get all mushed out of shape and are starting to crack. At least twice before, I've had to replace them when the left one -- the side of the engine that tries to lift under torque -- came apart.

I recently started noticing the familiar symptoms again and found that sure enough, the left mount had separated. This time, though, I wasn't able to find those mounts for sale anywhere. It's not like your normal parts catalog is even going to recognize the 351 engine, but this time even catalogs that showed other 351 parts seemed not to know anything about the mounts.

I ended up improvising. I found a pair of "universal" (and/or '72-'91 Jeep) motor mounts (#2.1102) in the Energy Suspension catalog that turned out to be almost the same size as the originals. All I had to do was file each of the mounting slots 3/16" longer to accept a pair of bolts 4" OC. I've only replaced one mount so far, the bad one. The new one is made of harder material than the original so I do feel more engine vibration now, but I can live with that.

Does anyone know of any other ways to get motor mounts that'll fit this application?

The 3.1108 mount (same catalog page) looks like an exact fit for my transmission. Is there anything I should know or check first?

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'68 GMC C2500 with 351 V6, Turbo Hydramatic 400A.

My other car is an '80 Honda Civic.