Please help with tire size

[chuck3026]

I will start by admitting I'm a dummy for getting this far and not having tire size figured out...with that being said can anyone help. I have a 72 stepside with a 67 front clip. No inner fenders and a set of 3" drop coils with 2 1/2 drop spindles out front. Rear is a leaf flip kit so I have dropped 5 1/2 and about 6. I have bought my wheels which are 20" 8 1/2 in front with 4 1/2 bs and 10" in back with 5" bs. The rims tuck fine but I'm concerned with tire cleareance/rubbing issues. I have seen 274/45/20 on alot of trucks all the way around but don't want the front tire too tall. Any advice is appreciated