Cannot directly answer your question but we recently had a problem with the tail housing on our 3-rail (pre-escort) gearbox in a SIII. We found that the gearbox support/fixing bracket is specific to a type of tailhousing/mounting bracket combination. Later combinations, wedge shaped fixing on the tailhousing, would make the tailhousing and gear change sit too high on our chassis. If your chassis is orginal SII, I suggest you look at the support bracket.