a 8" rim with 4.5" bs is exactly what you need. i ran that on my 67 for long time with a 245/60/15. had to trim 1/4" off the wheel lip because it would rub if i had fat girls in the back.
think you mean 5.5BS, here are the 16x8's with 4.5" BS, rear is perfect, front not so much! im going to have a 7/8" spacer made for the rear so i can run any of the 4 tires on any corner
here are 255/50-16's on my 73 swinger, only mods are 1" bars up front and 1 1/8 bar, in the rear is low arch SS springs (cant remember if its 003 or 002)