I have done it both ways. I had the rear housing for my build and ordered wheels to fit the car and housing, no spacers required. Fixing to narrow a housing to fit a set of wheels on a mini tub project that is totally custom. Guess you could look at it as the wheels are $1k each, housing and custom axles way cheaper. (if you can do the fabrication yourself) Both require a bunch of measuring and tripple checking.
