stock rims come in more than one width. I have run that size on the rear using 7" wide cop car wheels. Most mopar alloy wheels and some steel "road" wheels of the era were the same width.
I have 255-60-15 rear and 235-60-15 front on 7" rims on Modoba. Probably as big as I would go on a 7" rim. You could go bigger, but will likely have uneven wear issues. m2c