I don't know why one Advance would carry mounts and not another... My Advance has stock mounts for $14 each. That said, I have drilled them right through the steel, rubber, then other steel, then bolted them together. You have to use a nylock nut on the bolt so you can just barely tighten the parts together without the nut falling off. If you don't tighten it much, the rubber still insulates the same as before. You just can break the mount apart again is all. I suppose if you tighten the bolt too much, it will cause a loss of insulation from the rubber. I don't know. I did this mod out of need for a mount that wouldn't come apart. Not so much for a solid mount in the way that racers use them. Though, if your mount can't split or stretch, you get improved weight transfer.
I got mounts from Checker for $9.00 each. I then discovered that they are not as good as the originals (they don't have a safety pin), and since my new engine will make more power than the old one, I need to have at least as good as original mounts, so I took them back. The OEM mounts I ended up getting cost me double...
I don't know that parts america OWNS advance and checker... Advance is a company on its own, has its own stock, etc. Parts America is the online provider thingy for several parts companies, though, from what I understand. And yes, I now realize that we sell the stock rubber mounts through parts america, but we don't through the store itself. The mounts that I looked up in the computer at work were $14 something, but said on the screen that they were "solid". Same with the trans-mount.
Ive got both mounts here at my house. If you want them send me a PM. can have em both for $10. They were both brand new when I put the 302 in my car. Car ran in the driveway, but no actual miles on them.