I have tried two approaches for the rear rims.
#1) Original or RPM RC10 rear arms, with B4 rear hub carriers and B44 rear CVAs. You need to shave the B4 rear hub carriers to make it fit in the RC10 arm.
#2) Dynotech rear arms, with RC10GT rear hub carriers and B4 rear CVAs. (RPM also makes a GT rear hub which fits an oversized outer bearing for durability)
I believe both approaches have been discussed in this thread, but I want to consolidate both approaches, and my own experience with both, into a single post.
Technically speaking, both approaches work. The shock mounting holes on the Dynotech arms are positioned a bit differently than the RC10 arms (each hole is between the holes on the RC10 arms), though. So, with approach #2, you may be limited to the middle hole in terms of how far out you can go (at least if you're using big bore springs like I am), which is in between the middle and outer holes on the original arms.
I have found that with approach #1, you will need some downtravel limiters on the shocks to keep the B44 rear CVAs from coming out of the diff outdrives. It is a fairly uncommon occurrence, but it can and does occasionally happen given the enormous amount of droop. I have also found that, with approach #1, the rear is narrower than the front (if you use modern rims, and this is before applying the GT front axles to widen the front, which increases the front-to-rear width offset even further), and so you end up having to use B2/B3 rear rims to get the correct rear width. This is especially the case under full droop, where the rear wheels get pulled inward slightly. With the car at rest, the rear width is closer to the front (with modern rear rims), but still notably different (sorry...I do not have measurements at the moment).
You can still run modern rims if you want, but you will not be able to use the outer shock mounting hole on the arm (the shock will rub against the rim, but this is not the case if you use B2/B3 rear rims) and then you'll need even more downtravel limiters and you may end up compromising jumping performance as you go further inward with the bottom shock mounting hole. The following youtube link is me running my Team Car with a 17.5 motor, with approach #1, and with modern rims all around. I have Losi big bore springs (red front, yellow rear) and AE 30wt oil all around, with the rear shocks mounted in the bottom middle hole on repro RPM RC10 arms. In the front, I did not yet install the GT front axles, as at the time I was still running RPM front steering blocks, which are not inline. As you can see, it worked alright, although it did suffer from on-power push (this was with, I think, 15 deg castor blocks. I have since installed 30 deg blocks which should help address this problem).
http://www.youtube.com/watch?v=A7D7wisg67I
With approach #2, you can mount modern rims and the rear width is almost bang-on compared to an "original" setup. I happen to have both a Team Car (modernized) and a World's Car (not modernized) and so I was able to directly compare the two. Putting both cars back-to-back, the rear widths match very nicely. Since the GT rear hub carrier is slightly narrower, from the inside of the inner bearing to the outside of the outer bearing, than the B4 rear hub carrier, you will need one axle shim between the wheel axle and the inside bearing to eliminate slop between the drive pin and the axle spacer on the outside (this also pushes the dogbone into the diff outdrive a little bit, giving you a little more margin to keep the dogbone from popping out of the diff outdrive). One thing I did notice here is that, with approach #2, you cannot crank on the wheel nut to tighten the wheel down, as this will induce bind in the drivetrain. So you have to start by tightening the nut and then gradually backing off, while turning the wheel to check for resistance, until it rotates freely. This is not an issue, or as significant an issue, for approach #1, but so far as I can tell, this is the only real downside to approach #2.
At the front, I recently installed inline steering blocks with RC10GT axles (which have some offset, as discussed earlier in this thread). If you do this and install modern front rims, the front actually ends up being a little wider than the "original" front width. I think this is because the difference in wheel offset between vintage front rims and modern front rims is smaller than the offset provided by the GT front axles. So now the front ends up being wider than the rear by ~ 1/16". Presently I am running this setup and will test it on one of my local tracks in time (hard to find the right opportunity when I'm always running my B4.1 and B44 on the weekends). I did run this a little bit in my driveway with some beater tires and it felt pretty nice.
Theoretically speaking, I think approach #2 would be preferable, because the Dynotech arms are wider and this should reduce camber gain compared the original arms. Even though the GT rear hubs "reset" the rear width back to parity with the original rear width, the amount by which the hub offsets the wheel location, for the same camber link location, will not affect camber gain, and so you should be better off running a wider arm with smaller offset hubs (which increases the camber link length), as in approach #2. The only disadvantage here is that the GT rear hub carriers have one ballstud mounting hole for the camberlink, whether you use the AE part or the RPM part. So, your camber gain adjustability is not the same as if you used approach #1, where the B4 hub has three mounting hole positions. In most cases, it is probably not an issue, but on loamy, low grip tracks, you may want to revert to approach #1 to get a little more rear side bite.
)
