Most of these (Daihatsu HiJet, Suzuki Carry/Mazda Scrum and Mitsubishi Minicab) have the engine right behind the driver and either the driver sits on top of the wheels or, especially on newer models, the front wheels are pushed forward to the front corners of the cab. The rear driveshaft is very short. Here is a '95 Mitsubishi that has a dump in the up position to show what it looks like.
I imagine doing a longer driveshaft would not be too difficult.
Hondas (Acty) have the engine located just in front of the rear axle which might make for an interesting AWD midi setup.
Finally, Subarus (Sambar) have the engine just behind the rear axle. That would probably be even more flexible and suitable to make a fun run about with. Mini 911 C4 anyone?
They are, incidently, the only make that comes with a 4 cylinder. Some even come stock with a supercharger.
Suzuki and Daihatsus are far and away the most popular and easiest to find parts for. Then Mitsubishi, Subaru and finally Honda.
All Kei trucks are pretty much exactly the same size. Think original Suzuki Samurai. Not bad for two average sized people but small. I haven't been in a Miata in a couple of years but I think my truck is probably just a little narrower passenger hip-to-hip wise than that. They are legally limited to a maximum length of about 11 ft (3.4 m), a maximum width of 58 in (1.48 m) and a maximum height of 78 in (2.0 m) with a maximum displacement of 660 cc. Most of the newer (1999 and up) come with 4x100 bolt patterns which is nice. Before that time, there is a scattering of other bolt patterns. Also, all 1999 and newer trucks are fuel injected. Those before that are mostly carb'd.
Of course, just like anything, there is at least one North American based enthusiast forum for these trucks, http://www.minitrucktalk.com
if you want to find out even more.