[TR] Trunnions later TR4 with 3 degree caster

[Randall]

> So are you saying the TR4 had different links than either the 
> TR3 or the Tr4A-6?

No, the TR4 vertical links were the same as TR2-3.  When the caster was
added, the link itself did not change, only the location of it's upper end
relative to the lower end.  The A-arms, ball joint, trunnions, steering
levers, etc. all changed to tilt the link, but the link itself did not
change until the redesign with the TR4A.

Randall