rear suspension options?

i went from the stock 5 on 4 215/60R14 to 5 on 4.5 255/60R15 Mickey Thompson E.T Street S/S tires with US Wheel 15x7 with 4.5 back space. I got the bigger axles and green bearings from diff doctor. its the biggest wheel and tire combination i could find that fit the car with out tubing or flaring or shortening axle ect... i have about a inch of clearance from front tire to rear quarter panel.

espo springs and things website looks pretty good. i think i will try their leaf springs out. what do you think i should go with for rear shocks?

Recently i replaced the front shocks with the original style from napa. my deep sump oil pan is about 3-1/2" off the ground, and i had to make a bump stop to keep it from getting smashed into the ground when i come off the throttle, these replacement shocks helped, but i think they need to be something more. ill check it out after i get the rear done.

I had to get rid of the slapper bars because they were in the way of the new tire/rim combo. which might have to do with this whole situation. regardless they had to go due to clearance.

what is your guys opinion on the rubber differential bump stop...that seems odd to me... with the slapper bars and bump stop i had very little suspension movement before it would hit the bumper... my springs must be spaghetti. i think ill start there...which might help with the front end too.