I find the easiest way to refill the gearbox is to take the passenger floor and gearbox cover out and come at it from that way. For the transfer box, take the fill plug out on the back and fill from the inspection cover on top. Only thing is, after a couple of times doing it like that you'll probably want a new cork gasket as it'll start to seep. I want one of these things!
Filling gearbox,I take floor up and do it with a funnel that has a bit of hose on. Started doing it this way (and diffs) when I bought a new transmission oil gun that leaked, got another and that bugger leaked!
Ah, I use an old 1L EP oil bottle with one of them extendy nozzles - decanted into from one of my many 5L tubs of gear oil! I seem to get though a fair bit...