Frank, I'm guessing the wear 'may' be limited to a step at the end of the shaft bearing the brunt of the 1st / reverse gear cluster, if so it may be worth considering localised repairs by turning down the worn area of the shaft and sleeving it, then have the sleeve surface ground to size, that way you keep much of the original shaft intact and able to use a harder material for the bearing surface without going down the route of hardening the whole thing, it can save a lot of time and expense if needing to faff around drilling and plugging for oilways and boring out the core if it's a hollow tube type shaft!
An alternative to Nitriding if you do go down the remanufacture and hardening route is Tuftriding, which is a process using cyanide salts and probably more readily available (and affordable) as a process than Nitriding!
This is a process I've had done countless times on vulnerable crankshafts to cope with high RPM performance applications from Formula Fords to F5000 V8's and A Series Mini's to Boss Mustangs, the coating is very durable and I've never had a failure even on the infamous Triumph Stag cranks, you just need to take care when polishing the surface after treatment not to go too far and get under the coating which is relatively thin, but as a treatment, it's way more than adequate for your needs!
Check Yellow pages or run a Google search for Tuftride treatments or phone around a few performance engine builders, they'll know of a company that does it, and may even tuck your finished shaft in with another batch for the price of a pint!
When you rebuild the box, I'd highly recommend using a good anti-friction product to coat bearing surfaces during assembly and when refilling it!
Wynns and Slick 50 products are very good as is Molyslip, but that does tend to centrifuge out of the oil after a while, I swear by the stuff, and having recently driven 700 miles across France and the UK to get back home on a virtually destroyed gearbox with next to no oil in it due to something letting go and puncturing the case, I can tell you it does work!
Apologies in advance if I'm teaching Granny to suck eggs, but make sure too that the bronze bushes are in good nick or replaced, because with a damaged shaft the bushes will have wear too!
John