marmed

So im looking to order a new set of wheels for my 1995 1500 2 wheel drive. I currently have 20 x 8.5 and looking to go for 20 x 9. The company im going thru custom makes the wheel so i need to figure out the best backspacing. from what iv read 4.75 seems to be common. on the rear im looking for a little more of a negative offset. but dont want to roll fenders or worry about rubbing on the fender wells of the bed. what would be my best bet??