'67 vs.'71 spindles and wheel selection

[PLavelle]

I am converting my '67 stepside from front drum brakes (6-lug) to power disc brakes (5-lug) from a '71 setup. I need to find new wheels to match the wheels I have on the back. How will this change affect the backspacing of the new wheel I need to purchase relative to the backspacing of the old wheel to get the same look?

Thanks.