Everything is possible, the only limitation is your bank account
as well as the level of your skill and the limitations with the platform. Only so many engines will fit in there.
If you haven't been on the Real 4x4 forum or seen Vince's 303 check it out....
http://www.real4x4forums.com/PinzgauerBBS/index.php?sid=f44d098254cd1c2ff60031f12b62c34a
http://www.real4x4.com/
Vince was the first guy to bring in the Volvo's and was one of the first to bring in the Pinzies. I have not been on that forum or active in the Volvo/Pinz community in a long time so do not know if Vince is still doing importation, ect.
The 303 is a very good platform to build up for overlanding. As long as you can work on it yourself, have a good parts source, are not in a hurry to get somewhere and don't need lot's of axle travel it is in my top 5 list of best truck the world has ever seen for overlanding.
Since there was some talk about engine swaps and such....
Obviously space will be the limiting factor. Not only for the area you have to work with in the engine compartment but also for things like oil pan clearance on the axle, room for exhaust and so forth. If you are taking on a swap in a C303 you shouldn't have to many issues dealing with the small things though like moving the axle for clearance or modifying the suspension to suit the other mods. I would take a long hard look at the Cummins/Isuzu diesels as well as at the smaller Toyota and Nissan diesels. Thing is you are going to want to stick with an engine that is easy to get parts for, has the power band and torque curve you want in this truck as well as tranny considerations. I myself would avoid a swap that involved mating the engine to the stock gear boxes. If it was me I would go for the Cummins/Isuzu or Toyota engine and then run a domestic tranny/t-case or toyota boxes. Correct me if I am wrong but the front axle is passenger offset and the rear is mostly centered? If that is the case a variety of Toyota or domestic gear boxes will work no problem. If suspension becomes a problem because of clearance issues and so forth, well these trucks are a ladder frame so not to big of a deal to customize the suspension to suit whatever else you are doing. The lockers are vacuum operated so very easy to adapt that over to be supplied by a new source/system. As far as engine and gear box mounts, if you are doing the motor swap you should not have an issues coming up with and fabbing those.
If it was me and I bought one, first thing I would do is make sure it is all sealed up and rust proofed. Then I would get all the mechanicals in order. Then I would kit it out for overlanding/offroading. After that I would do a few small mods like upgrade the CVs and do disk brakes all around. After that I would use it for awhile. If I decided I wanted a different motor I would look long and hard at the ones I mentioned and it would all come down to what is going to fit.
I also see a little talk about suspension in the thread...
It should be no problem at all to have Alcan or Deaver or a few other places make you leaf springs, in particular ones that will use an easy to find bushings. Or for that matter I can not see why it would be all that hard to fit a linked coil spring suspension under it, even with coilovers. One of the problems with a Pinzie and modifying, actually
the problem, is you don't have a ladder frame and solid axles to work with. The Volvo this is not the case.
One thing is for sure...I would love to see a C303 or TGB with a diesel swap and different gear boxes. Not to mention one with some suspension mods. So if anyone does it or has pictures post them up!