Those rear wheels in the photo do seem to protrude and may come to grief in some states or inspection authority. I had that problem with VWW. They may fit other cars or even some Harrisons fine, however.
If you go to the Dragway site (
Classic Wheels ) and then their Offset Chart you get a useful diagram with the necessary measurements.
I used measurements that I derived from other owners of Harrisons. They all vary in the way that the chassis sits on the frame (L-R), rim and tyre dimensions and the type of suspension fitted (typically R32 or R33) and also with how the suspension is set up.
On the chart (above) measure all four wheels carefully with a ruler and straight edge and determine the required measurements that keep the eventual tyre (17" or 18"s) within the 'guard edge and not hitting any suspension or brake components on the inside. Take your time with this step as it is the most important. Then talk to Dragway or another provider.
For my 17"x 8" rims, I eventually used a front space of 78mm on the Front and for the 17' x 9.5" on the Rear, 94mm. Fit is perfect, even with my larger AP brake calipers and disks. You can determine backspace as well using the diagram for a known rim width.
Not sure what bolt/stud pattern that you will have but they vary from front to rear on some Harrisons (GM/Ford/Nissan). I made mine all the Ford/Nissan pattern for convenience.
Also see:
Harrison Cobra Rear Wheel offset