I also had the 185/4-1/2" combination that JPS touts as a solution for an IRS rear-end on a classic (non-flared) body. I agree with Terry's analysis.
The idea that putting down more rubber cures all ills is a fallacy. My 2002 JPS had not enough room for a credit card to be slid between the LR sidewall and inner fender. Couple a flexible sidewall with clearances that tight, and it's just a bad idea.
Terry corrected the problem by switching wheels to something with more width and back-spacing than the steel wheels. Just putting a smaller tire on it to start with is the right way to handle the issue of what to do with 4-1/2" rims.