If you want some really close coupling, try the extremely short shank Rapidos that LL used between the plastic frame FA-FB-2s. As for the front, 1134 (the long shank version of 1133). One thing that I have found on these, though, is that you must really work the replacement coupler box back into the slots on the tongue of the truck mount. At the same time, you must take care not to break the nubs on the MT coupler box.
Another solution is to use the original knuckle couplers that came on the C-C corrugated cars. Remember? Those funny shaped brown things that were worse than the MDC knuckle couplers? Funny thing, they do stay coupled to MTs, AccuMates, MicroMates and Unimates, as well as to the various 'dummy' knuckle couplers sold by B-mann and LL. You do have to work them onto Unimates, though.