Hi Jeff,
Had to go look and see what car you are working on.
TR6 can definitely benefit from a shock conversion, as can all the IRS cars.
With TR2/3/4 and the live axle version of TR4A, I'd think twice about it... Lever shocks can be made to work pretty well with multi-leaf springs.
An exception would be any of the live axle cars that have been converted to a monoleaf suspension, in which case tube shocks would probably be best.
Racetorations stuff is generally good.
The Revington TR kit uses a different method of positioning the shock, that some folks like better. But it does require some modifications and welding.
There are other, steel kits similar to Racetorations, but heavier of course.
Basically, what I'd watch out for in any conversion would be that it must attach to the frame, not just to the body. Any kit that's relying only on the sheetmetal of the body to support the shock is going to be pretty short-lived.(Racetorations attaches to both, which is okay.)