You're far better off doing it yourself. Specialists in the UK typically charge £3-400 for a recon main box, but if you have a lot of damaged shafts, gears or synchro hubs, the parts alone cost this much, so they clearly make their money by turning out scrap. It's not unheard of for them to nick the good components from a box and replace them with worn parts. There are some good companies, but they're few and far between and cost far more.
The OD is separate, and unless it's playing up, I'd leave it alone. Just take it off and leave to one side while you're working on the rest. Have a close look at the clutch sleeve splines though, as they're very fine and do wear.
www.legs.co.uk sell overhaul kits for a little under £100. These include all the bearings, seals, gaskets, shims, bushes and synchro cones for the main box, and the quality seemed fine when I rebuilt mine this year. They also stock all the other bits you might need.
You need to partly dismantle the transfer box to strip the main box. The output shafts and bearings are usually OK. The intermediate cluster bushes and bearings would best be replaced, especially as the cluster comes out during the strip down anyway. The bearings are one size (2 of), but the 2 thrust bushes come in different thicknesses, so you'd need to order the right set (may be marked on the old ones, otherwise use feeler guages to work out what thickness you need).
Wholesome, oily fun that will ensure you have a perfect transmission in a few of days work (including removal and re-installation), for a fraction of the price of a properly professionally rebuilt unit.
