I would clean it before putting it in, if possible. Also, don't leave the gears set without oil on them (after cleaning) they will start rusting overnight.
Wrenchbender is right about torquing the pinion nut. Book calls for 160-240 ft-lbs, iirc. But that is only needed for the initial trunnion install, when it was new. Besst thing to do, if the nut hasn't been loosened, is to use a center punch and mark the nut and the end of the shaft. That way you know where to turn the nut to when it goes back on.
To loosen the nut without an impact wrench a big pipe wrench and cheater is usually needed. I think the nut takes a 1-5/8" socket, and it needs to be thin walled, not an impact socket.
