B body rear,

I'm not sure if I could get measurements from an A body 8/34, say the inside of the flange to the original center hole of the original perches then use that measurement to locate the new perches while on jack stands on the floor. I guess all I have to do is use a level on the perches before tack welding them on the housing, but getting the initial measurement on location would be the first step. I looked at different measurements on this site and others which are all seam about the same, but in my situation they don't help. Using your method does seem logical as a reference point.