Best Place to Buy Motor Mounts For my 383 Formula S.

Polylocks suck in my experience. I have an original 383 car with headers. The passenger side mount 'melted' three times, Schumacher replaced it each time no charge. I fabricated a heat shield two different times, same result. The torque strap doesn't fit 383 cars, as you found out, so I bolted a chain to the engine, that didn't work either.
The polylocks are designed to 'lock' in place, they will not pull apart, but they will slide apart, if that makes sense. I could see the poly stretching and the motor got lower on the passenger side.
For the passenger mount, I ended up drilling a hole through the mount and putting a bolt in, however there isn't enough room for the bolt to stick out the bottom and get a nut on the end. It has held for some time though.
Now I see for the first time, the driver's side mount is 'melting' the same as the other side. It is clearly not caused by heat, that mount is way forward of the exhaust.
I ordered solid mounts from Summit, for a B Body I believe, this gets me the passenger mount, and solid mounts for a small block, if I recall correctly. This is for the driver's side, not a bolt on like the passenger side, but it is the correct size and shape.
Just need an afternoon to modify the one and replace both. I'm leaving the poly tranny mount so I don't break the transmission.
With the polylocks, the engine never moved, and still doesn't when driving, easy to tell as I have a tunnel ram, so I am not worried about the solid mounts.
For what its worth, it's a four speed car, however I don't do burnouts or beat the heck out of it. I do drive it regularly though and enjoy it.