A500/A518 to Gen-III

Doing my research on my Gen-III to 71 Demon swap. At this point, I plan on using an A500, however finding details on if there is a swap type flex-plate needed. Any insights would be of great assistance.

At this point, I plan on using the US Car Tool cross member, and may need to trim the tunnel. I seen a few OD Switch's or setting up to vacuum (not sure on this part yet either).

Thanks in advance