To be honest, if you have a manual, just reading it will mean you understand what your mate says about a certain bit.... would help I suspect
Like others here are saying, it could well just be the linkage, rather than the actual box going AWOL, so rather than being expensive, I think your mate just needs to know where things are supposed to be, and what is missing.
I don't *need* a manual for most mechanical work, but when you need torque settings and are trying to piece something back together which has fallen apart, sometimes the odd picture or exploded diagram solves your problem in minutes rather than hours.
Every car I have ever owned, I have bought a Haynes for, or been given one, or have sourced a pukka original workshop manual, either on CD or book form..... more to learn about how different manufacturers do different things -it might fill my brain with SOME worthless information, but a lot of it *IS* useful, and can help at flash diagnosing a fault should one occur......
Get a manual, you know it makes sense
Bowie.
P.s. don't EVER drive it like that again, 2 small wheels, 2 large, if you transfer box isn't already broken, it will be pretty soon! as well as you UJ's, Diffs etc.... get it working right first, then start bolting the goodies onto it.