In regards to 4sp vs 5, based on my experience it's a bit of a toss up - strictly related to road racing, unless an actual Nissan comp unit (opt 2) is used, and good luck finding one relatively cheaply. The "close ratio" fs5w71b found in the 80-83 ZX's is really a wide ratio, hence the "w" in the part number, and there's no getting around that. The 1-4 ratios on both the 4 and 5 speeds are for practical purposes the same with 3rd and 4th identical. The problem with using such a numerically high final is you essential move up the "primarily used gears" from 2-4 to 3-5, and 5th IMO is the weak link of the trans. Using the later zx trans as a baseline (1.858, 1.308, 1, 0.745), your final drive ratios with the 4.3 diff are: 3rd - 7.9894 4th - 4.3 5th - 3.2035 the same trans with 3.70's: 2nd - 6.8746 3rd - 4.8396 4th - 3.70 I've raced with a 3.70 final since day one (primarily at Blackhawk Farms) and for the most part I only use 2nd at race starts or when slowed by lapped traffic. Depending on the race start speed, which will most likely be the slowest you will go all session, rpm's in 3rd might already be a little too high with a 4.3 final, and depending on the track, a little too low at max speed. You can use an R200, but there is a valid argument for the R180 based on weight savings alone as it is significant. Regarding the CV halfshafts, I would say if you stick by SVRA rules you will for the most part be allowed into all vintage clubs. With that said they list half shafts as "free"