B13/B14 trans are definitely interchangeable, I've got a B13 Sentra trans on my B14 GA block right now. Only issue is you won't be able to use your CPS if you have a B14 (which doesn't matter, the ECU only uses the CPS when there is a misfire). I think the gearing is slightly different too. The sensors are pretty much the same, except B14 is electronic. Just swap it out for whatever car you're gonna use, i.e. if you're using a B13 trans swap the mechanical out for the B14's electric, and vice versa. That's pretty much it, they're the same housing/everything except for on the B13 there's no hole for the CPS to bolt into, which isn't that big of a deal.
CPS is the crankshaft position sensor iirc, and the ECU uses it only when there's a misfire. You won't have an electrical connector for it so don't worry about it.
The electrical/mechanical speedo sensor, all you have to do when you swap the 200sx's trans over to the B13's is swap the speedo sensor from the B13's trans with the one from the 200sx's and you should be good to go.