They went between the sway bar plate and the perch if I remember correctly. I need to try a different angle shim so I'll be able to verify that when I get back in there and swap em out.
A note: FMJ's use a large hole (as seen by the spacer, as shown), so your alignment shim holes will need to be enlarged a notch (or a dozen).
In this case, the forum member was getting rid of the weak ISO-clamps and going with an older, and much stronger, shock plate (below) and needed something to keep the differential located in place.
Finally got a chance to swap out the shims today..it only too about an hour and a half, most of that time fighting with the DS trying to get it lined up with the perch until finally just dropping the axle onto the spring.
Going from 6° to 4° seemed to fix it...and I am quite happy about that. Now, Dad seems to be a bit more motivated to keep it, and continue making it the street/strip toy I was going for.