205/60s or maybe 215/55 is the widest tyre you can squeeze under a std rear arch and they would fit 6.5wide rim.
The other concern is trying to find an 8 inch wide rim to weld the wide 5 centre into. Been a fair few 14inch wide 5s done like this but not seen a 15inch wide 5 over here and banding is illegal in Oz.
madness is in the eye of the beholder 👍
Yuo probably would be able to squeeze a 8" rim on your car, there a few problems that you will run into, if it is a steel rim the increase in unsprung weight will cause a reduction in ride quality and possibly the handleing will suffer, being a light car they do not like a heavy wheel, and tyre combination, the two photos show a my convertable which is a long axle car fitted with a 8.5" porsche wheel and a 255-45-17 tyre, the tyre just touched the trailing arm bolts but would probably rub on the guard, the next photo shows the same car with a porsche 7" rim fitted with a 225-50=16 tyre, both wheels have a ET of +40mm, find how much shorter the axles are on a early car compaired to a late car and take it of the ET, this will be the offset for your car, a 7" rim will fit comfortably under the standard guard with a 225 or even a 235 tyre.
