If the rear main seal hasn't been changed within the last 50,000 miles it's a no-brainer to do it now, it'll only take you an extra half hour, tops, and it's cheap. I'd suggest getting that from the dealer though, too many of the aftermarket ones are such a sloppy fit that they'll literally pop out of the seal housing if the flame trap gets plugged. I'm not sure about the torque converter - I've never had to put one back in. The key there as I understand it is to make sure the torque converter splines are aligned correctly on the driveshaft for the pump upon reassembly. And if that shaft seized into the torque converter and pulled out of the pump - located at the back of the transmission - that's the really nasty issue to remedy. So as long as the shaft to drive the pump is intact in the new transmission, and your old torque converter is the same type (ie, locking or non-locking, as designated by an 'L' at the end of the transmission name, AW70L for example is locking) then you should be alright. Just take your time and make sure it's fully seated on the shaft, or things will break when you tighten up the bellhousing bolts.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina