wich gearbox is better the stock one or butterbox??
I haven't driven a civilian International, but I can say that there is nothing wrong with the AACO gearboxes, whichever model you buy.
If you get one with a petrol engine, I think this vehicle would be an ideal candidate for an LPG conversion. The tanks could be disguised if necessary somewhere on the machine. Petrol at over $2/litre, is becoming too ridiculous to consider anymore.
In an earlier post you asked about the petrol engine's reliability. I drove them for 5 years in the Army Reserve and the only troubles I had were;
1. Fuel vaporisation on hot days. This could be fixed by using an electric pump near the tanks.
2. Radiator fan bending the water pump shaft and destroying the radiator. This was apparently a common problem and could be fixed by; substituting a lightweight modern fan; or removing it completely and using thermatic fans.
Brake parts can be re-conditioned when they wear out, by sleeving cylinders and re-lining shoes. The air side of the brake-system I know little about.
Good luck with your search,
Cheers Charlie