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As mentioned above, the 73 to 79 4x4 was never available with a 460. You are looking for something that does not exist. For those of us that have installed the 385 series engine, we have kept the factory stuff and used an aftermarket rubber (or solid, or combination of two) like the L&L units.
Not real expensive, and easy as pie for your conversion.
I use the L&L's on one sideof the truck, and I use a solid mount on the driver side. My truck is a 4x4, and uses spherical rod ends on the steering componenents, so vibration is a natural part of driving my truck. Even Though I run a 557 cubic inch BBF, it does not vibrate that bad.
I also use the L&L headers, so clearance is not an issue. I also use a Gear reduction style "Mini" starter, and I have clearance for days. The L&L's also help with my trucks that have hydraulic clutches. Nice headers with big flanges, no leaks.
They are a little short, and do not make as much power as some of the other longer ones, but this is minimal, and the clearance advantage far outweighs the slight lack of power.
I'm running the Autofab conversion mounts. It replaces the factory towers and uses a captured Poly mount. They do transmit a more vibration than stock. They are well built. I believe they are also available through Advance Adapters. Here's a picture of them as delivered.