Other than the stock the most significant, and diagnostic, difference is the RT's single stage trigger.
Latter versions also sported a cocking lever with a cranked knob (). Presumably this was to make access to the handle more assured in a discipline shot against the clock.
The muzzle weight also lacked the cutout for the front sight, hence the small weight difference compared to the regular versions (10 and 30g respectively).
Lots of good info on the Vintage Airgun Gallery, model specific section and the LGR Manual.