These adapters from CT Newman Engineering are made to be used with a 67-72 Harley Davidson big twin hub and hydraulic rear drum brake. These will allow you to run a car wheel with either 5 x 4.5" or 5 x 4.75" bolt patterns. They are machined from 6061 aluminum and already have a sealed bearing and retaining clip installed, bolt on an go!
For a baseline, on an OEM mid star juice drum setup with a round swing arm and stock spacers a 3.5" wide wheel with 1.375" backspacing will pretty much be centered. There are LOTS of options when you start playing with different wheel widths, backspacing and spacers so please do you research before hand and feel free to ask any questions before purchasing.