There are actually several differences between USDM and JDM Supras. USDM has larger injectors, but smaller turbine and compressor, and also, TT Supras ONLY came with targa tops on the automatics! Sooo shitty! A few more differences I remember are cam size/duration, the use of a MAP sensor (as opposed to the MAF sensor on USDM Supras), the larger A/R ratio on USDMs, a higher differential ratio on JDMs, differing TCS's, and a few wheel and tire differences before '95. I think with the larger turbine and higher diff. ratio, the JDM may be a better BASE for BPU+++++PLUS++, but I'd miss the targa.
It should also be noted that the Supra was down 40 HP compared to the USDM version, but had 8 more HP (23 more on '97 VVTis).
By the way, 'being JDM' with RHD (the perfect formula for flyest guy in town!) isn't the only reason to get a JDM Supra at all. Over there, F&F didn't jack the prices above what they should be, so you can get a '97 TT 6SP with about 60K miles for around 15-17K, and if you just want the hawt look of a Supra for your daughter, a '93-'94 NA Auto can be picked up for 8-9K (I shop Supras in Japan often!). Also, with higher gas prices, more crowded roads, and more practical mass transit systems, Supras WILL have lower mileage. Under 50K miles is NOT hard to find. There are also less straightaways and more traffic density on narrower roads in Japan, so less oppurtunity to "get on it," insuring a less-redlined 2JZ. As I said before, hardtops are also easier to find there, which is choice for the big-time performance enthusiast. Also, the fact that the Supra was manufactured until 2002 in Japan means you can get a newer model, which is always mo' gooder.
The USDM Supra is not superior to the JDM model, just given a few differences for more HP. In either country, the car was made to be tuned, just as any Japanese sports car is, however Americans would never pay that much for a <300 HP car.
As was said before, try a search, but that shit can be frustrating, but I'm pretty sure importing and USifying a car is pretty painless as long as that model/trim/year is manufactured stateside already. Your best bet would be to give me the money to try it myself.