As you found out the front T bars are much stiffer than the rear leafs so adding extra load on the front will tweak the rear more than the front .
The T bars will have #s cast into the ends so if you clean the rear you should be able to see the #s , typically you will have 77 / 78 T bars odd being the left side , if the adjustment bolts are off a bit but the car rides fine , no need to swap T bars .
All the advice here is good , make sure you have the ride height where you want it , do not get it aligned to factory specs , they are for Bias ply tires , max the caster & 1/2* negative camber & 1/16" toe in & you are good to go
