Hello,
You may have come across this already, but THE website for 101s is:
http://www.101fc.net
or more specifically, if you want one with big wheels:
http://www.101fc.net/grumble/index.htm
As to where you go about getting the wheels from, I don't know. I know that military surplus places are a good source of replacement tyres for 101s, so maybe its worth seeing if they have any wheels off something else with the same stud pattern (maybe something like a Pinzgauer???). I'm sure someone at 101fc.net will be able to help you.
I doubt there are any 'off-the-shelf' suspension kits for 101s, since they're specialist vehicles and they have unique chassis, springs and axles. Land Rover Owner International did a feature a little while back on a 101 that had been fitted with rear coil springs
as well as the standard parabolics.
As you say, there are some out there on coils- I imagine it must be possible to fabricate something using various parts from other Land Rovers.
I'm not sure I'd bother with altering the suspension though- my experience (not a lot, granted) with 101s is that they're just as good as any other Land Rover when it comes to the rough stuff- the on-road ride is terrible when they're unladen, but that's the downside of having a heavy-duty vehicle.
Engine swaps to Tdi are definitly possible, most of the ones I have seen have used a complete engine+gearbox from a later Land Rover.
Td5 must be theoretically possible, but like putting it anything else, wiring up all the electronics is the real snag. If you want a challenge though, it would be a good project.
Most diesel conversions seem to go for the bigger Japanese stuff (usually in the 3.0 - 5.0 litre range, or if you really want, the GMC V8 diesels go very nicely.
I don't think there's any 'by the book' method to modifying 101s- its very much down to what the owner wants to do and how they want to do it.
Jack
