spring relocation

Before you under take moving the springs inboard, why don't you try some new springs and an adjustable snubber or cal-tracs.

You can buy SS springs and an adjustable pinion snubber with new longer shocks for $350 of bolt on parts. A set of caltracs with the Caltrac springs will cost more ($600-700) but a lot of racers swear by them. Either one of these setup will work much better than stock springs and pinion snubber.
How close is the top of your pinion snubber from the floor of the car? Mine is adjusted so it has less than 1/2" gap. If you have a hard launching automatic or a stick car it is supposed to be adjusted so there is no gap between them.

Either one of these upgrades is stuff you will need on the car even if you relocate springs at a later date.

just my $.02

Bob