look at the mounts. I think it is a plain ol 500 (yeah plain LOL) the transaxle is funky. It bolts like a regualer trans and has a revrse shaft to the front and couples to a big pumpkin that runs the CV axles.
It should fit right in a rear wheel application.
I would check the block for mount bosses and compare to another 500 if you can . I am thinking they are all the same.
Fact is stranger than Fiction