another wheel ?

[natechevy72]

OK. I was going to run 17" torq thrust 2 wheels on my truck, but I am now thinking of changing to the 18" Foose Nitrous wheels. It says they have a 4.5" backspacing. Will this be ok? The truck will also be running a 4/6 drop kit. It is a 70 chevy short bed and I was going to switch out the rear end to a 71-72 rearend for 5 lug. What would be better changing out the rear end or having the axles re-drilled. Thanks for all your help, Nathan