SBP Steel wheels: How to tell if 5.5 or 6.5?

VDART said
sbp only came in 4.5 & 5.5" versions 14" I do not think any other steel was made-- the ralleys I'm not sure on, Lawrence

You are correct and the sbp ralleys are 5.5" also. There was never a 6.5" OEM factory wheel for sbp according to Hollander interchange.