I don't like those biscuits mounts on anything more than a stock ish application. After going to drag radials
that type of Mount just wouldn't last. As far as installation goes they do sit offset like yours. I put solid biscuit type in mine I have had no problem since.
Torque straps are a must, I've been doing big block A-body swaps since the late 70's, actually was one of the few to weld up swap mounts and use the b-body headers.