I would be very curious why the mech. thinks it needs shims. Ask him to explain how the measurements were made. There are no shims in the stock factory configuration, just a choice of three different "Distance Pieces" stampled A, B and C. I've personnally never seen anything other than 'B"'s.
If shims are needed, you either find a different strut housing or make shims. Or have a new piece of pipe made to make a distanct piece that is the right length as mentioned above. This is basic machine shop stuff. Shim stock is nearly free.
Another thought, for 240 stubs, you will often find a copper "shim" on top of the inner bearing between the inner axle flange and the bearing.This is not a spacer, it is (I've heard it here!) a noise reducing trick. It has nothing to do with positioning the bearings in the races.