I picked up a very very dilapidated C-Car recently, and I'm beginning the restoration process.  The tires are completely destroyed, and the wheels are in really bad shape after dragging the car onto a trailer. 

The car is being kept in a friend's cnc workshop at his second property while I try and get it roadworthy, and I need to get it rolling ASAP so he can push it around the shop to keep it out of the way. It seems like there's a lot of conflicting info on wheels out there.  I'm looking for something I can mount a 175/50R/13 to ideally.  There's lots of cheap steel wheels from Summit racing, but I'm not sure what backspacing to get.  I know I need 4x4/4x100mm bolt spacing.  I've found a 5.5 inch wheel, but I need to know the backspacing.

End goals for the car are to convert it to a brush-less motor with regenerative braking, lithium batteries, and just generally modernize it.  We intend to use it as our weekly errand runner, and post office runner for our online business. We also have a 1975 International Harvester Pickup in our fleet, so we really need to offset all that polution!  We live on a hill in one of the windiest parts of the country, so the plan is to charge it off a couple windmills in our back yard.