Been browsing a while but this is my first post

I got me a HL Panzer III, just bought some heavy duty gearboxes and asiatam wheels from Forgebear, an aluminium hull from Welsh dragon and also got hold of some metal tracks too

Problem is I can't seem get the damn gearboxes to fit the new hull!! I have 2 problems 1 is that although all the important holes seem to line up, I can't get at them too well to tighten the screws as they are under the cogs!! Is it important to screw them all in or can I get away with just the ones I can get to? The second problem is the part where the sprockets attach to the gearboxes one of them is longer by about a centimetre than the other is there a way around it or should I talk to forgebear?
On a lighter note I don't seem to be having any problems with the electronics hehe!
Thanks guys!!