Ok...so this is what I'm workin' with

[69 Okie Truck]

A '69 C-10 LWB with leaf springs, amd overload or helper springs to back that up.

I've got 15 X 8 inch rallies that suit me jes' fine, but would like to fill the wheel well up with more tire. I'm past the slammin' stage these days, and wanna keep my truck...well...a truck. So that leaves me really with just one option, slappin' bigger meat on these rallies. Anyone got an idea of how much I might be able to fill those wells in with some beefier tires? Heck, anyone got any suggestions for tires that might do the trick? Am I limited by the 8 inch width of the rims?

I'm a long haul trucker, and only drive my personal vehicles every couple of months or so when I come in, and even then it's mostly my bike I'm on, so I'm not real concerned about road noise or tire wear in the pickup. I doubt I do 5k miles a year in the thing. Any suggestions?