Some other obvious points I guess I should make re deep dish wheels on an IRS:

The bending moment on the hubs and bearings, due to car weight, will potentially be much greater than in the stock application for which those parts are designed.



Braking will also cause some deflection steer, but less so because weight, and therefore traction, is transferred away from the rear wheels.

Solid axles, because of their basic design, will not suffer from such deflection effects to anything like the same degree.

IMO, if you're going to use an OEM IRS setup, particularly on a high performance application (lots of street rods are not actually driven in a high performance manner), you should try to keep all of the design parameters as close to stock as possible, to avoid the dreaded "unintended consequences".