I do know that guys who use the G50 over the 915, do it in large part because the G50 uses a hydraulic clutch. I know a guy who converted his 915 to hydraulic because he had a lot more options in terms of gears AND R&Ps. These options are also much more affordable as well. You can find new ring and pinions for G50s, but as one knowledgable fellow put it, "they cost absolutely stupid money." Gear sets don't cost as much as the R&P, but they ain't cheap either. I could put G50/50 gearsets in my G50, but it was much more cost effective to buy a G50/50. Only took 3 years to find one though /ubbthreads/images/graemlins/wink.gif
To my knowledge, the only issues with inverting a G50 is getting the fluid level right so it oils well. It does take a bit more gear oil, but the cost is a nit. The other issue is that once you get the proper oil level, the input shaft and, of course, the seal is under the oil level. If you have a bad seal, your going to have a bad leak. So, you put a new seal in it to begin with. The speedo pick up is also under the oil level. Everyone has said that the oil does not interfere with the magnetic fields and this makes sense. But, if there are ferrous particles they can build up on the pickup and this WILL interfere with its operation. Of course, if you have that much ferrous metal in your oil, you probably have bigger problems. An inverted G50 does lower the engine, but is that a bad thing? I think it is a good thing; my GT-40 oil pan is flush with the bottom of the car. I don't know what the issues with inverting a 915 are; possibly the flow back issue that Mike mentioned. At worst, this would require drilling ports between the sections I would think.