Rear output shaft seal

My rear output shaft seal needs replacing, did the front a while ago but put the rear off. Drum comes off ok. Can I slide the drum back and tie the prop up then take off the flange and lever the seal out with the speedo / seal housing still attached to the gear box or does that housing have to come off? If I leave the housing on is there enough room with the brake back plate on or does that have to come off (with the shoes on)? Is there enough room with the prop tied out the way or does that have to come off? I'm trying to work out what parts and how long to allow. Prop is good, bolts all undo, brake is good so I'm hoping to get away with just the seal, its all about the least dismantling. Thanks!

leave back plate in place though removing makes it easier, prise seal out and fill rear of new seal with grease or vaseline etc to hold garter spring in place while tapping home

+ 1 on the above,tie front end of prop out of the way,remove drum,remove flange and check where the seal run's.[ gearbox ones are usualy ok ]

Guys thanks for the advice, never thought of packing seal so that could be a real time saver! I'm hoping the flange nut is easier to get off than the front, that was a real pig, heat plus a very long bar.

Did this yesterday and its cured the leak. Seal was very worn and the nut on the output flange was slightly loose. No felt under the nut and the prop flange was filling up with oil. Hopefully now the transfer box will keep its oil in. Only problem was I didn't park on a steep enough slope and did the whole job with oil dripping down my arm. Seal running area was worn to about 1/8" wide, I wonder what mileage that would be?