Yes, unclued, TRAMCARS is correct: 'short race' = RAC (a bit uninspiring), which goes inside SMART ('quick'). Then you have to 'review' the whole thing, an uncommon but allowable indicator of reversal.
Can't help with 21ac though. It's my last unsolved clue, and the range of the three cross-checked coded letters is too wide to allow working backwards to arrive at the clue answer. Will someone please give a hint? Actually, will someone just spell it out?