Rear coilover kits and tire size limitations?

[siggyfreud]

Looks like from the wheel mounting surface I have about 6" of frontspacing, and 9.5" of backspacing, for a total of about 15.5" of width area for a wheel and tire. Also looks like I have a few extra inches beyond that for suspension, however with the way the previous owner ran the exhaust (outside frame rails) I'd have to redo the exhaust to make room for coilovers, which isn't a huge deal.