I found this info on the internet...
"1. The stock 2500m suffers from terrible bump steer. Bump steer is a change in the direction that the wheel is pointing (with NO input from the steering wheel) during suspension travel. The main cause of the bump steer is the stock TR6 steering arms. They cause a steep angle between the steering rack and the tie rod end,. To cure, use the 'shallow droop' TR4 steering arms (not all TR4 arms are alike). It is likely that TVR designed the suspension geometry with the TR4 part in mind, then some clever soul changed to TR6 parts without consulting anybody..."
Which steering arm is the "shallow droop" one is anybody's guess. BTW, Moss lists THREE sets of steering arms for the TR4. The earliest set seems to end when Triumph went to the 3 deg caster, so that one would be the rarest. I guess you would need to see all three together. Also, Moss has all of them listed as not available.