Rear ended moving around, need some tips.

So I swapped an explorer 8.8 into my 64 barracuda. Install went well and all that but, I noticed that my aftermarket spring perches that I bought on eBay have a bigger hole on the perch, than the size of the leaf spring centering pin. So upon test driving the rear end the other day, when I pulled back into my garage I noticed that the rear end is moved, passenger side seems to be in the same spot but the other side is back by 1/2" or so.

Does anyone know how I can remedy this?

I've considered removing the rear and welding up the hole and re drill as required but that's just not really practical and the perch metal is thick. Too thick for my mig 140

If anyone has any ideas on how to deal with this, it would be appreciated!