Good info and I do appreciate your input Whitetop.
I'm just out in the shop today tearing into my 68 to convert the drive train to a hotrod setup. Just finished saving the original style exhaust and was looking at wheel/tire clearances under there while it's on the rack. Looks like the 275/60's on the 8" Torque Thrusts have an inch clearance to the shock mounts and good clearance back towards the springs but then I looked up in the wheel house to see they have rubbed a couple times up high on the inner wheel tub. If I go any deeper to the inside they're gonna rub more unless I stiffen up the back suspension a ton. (not thinking of doing that)
If I add 8.5 Centerline rims out back and maybe I can fit them with L60's mounted up. Centerline 8.5" come with 3.315 BS if I remember right. I'm thinking those would allow enough clearance while the L60's wouldn't have too much sidewall projection off the rim? I'll measure the B/S on the current rims later tonight. Getting ready to pull the motor this afternoon and ready to unbutton the motor right after lunch here. More when I have measured the current rims to see what they have for backspace.