Hi George,
Have you seen this site
http://www.afv-model.com/4711shop/in...c54_Axles.html ?
They seem to have a more military vehicle "bent".
As for locked vs. open axles (I'm assuming you mean the differentials), if you intend to drive "on-road" or generally non-slippery surfaces, open is better.
Locked differentials are really for situations where you expect to lift one or two wheels in the air (open diffs will direct all power to the free-spinning wheel).
Ken