Got the MC16 torn down into assemblies (and carried it into my apartment), and it is a bit rough. It was a nice bike at some point, but it probably sat in a field for some time. The seals are shot, the brake pistons are shot (side note, just found out that MC16 is a bit unique with running dual piston rear brakes; everything else after that uses single pistons), the subframe is trash, and there's a lot of rust, but there are some positives too.

The engine looks a bit dirty, but in good shape (besides some surface rust on the ignition rotor), it spins, there is compression, and the pistons looked clean from what I could see through the exhaust ports, even had oil and coolant still in it. The guy did say that he was working on getting it running before he sold it, so I assume that he was focusing on getting the engine running first and left the rest of the bike for later, before putting it up for sale.

Another positive is that one of the aspects of the RS250 swingarm swap might work out. I did some quick and dirty measurements of the opening of the swingarms that I had on hand, and MC16 is 205mm, RS250 is 200mm, and CBR250RR MC22 is 210mm. So I would need to find 5mm to fit MC16 bits in the RS250 swingarm, but the nice thing is that the chain tensioners on the MC16 and MC22 straddle both sides of the swingarm (as opposed to going inside on the RS250 swingarm), and they are 3mm thick, so removing them means that the MC16 bits should fit perfectly in between the RS250 swingarm (no idea about how centered it will be). The jury is still out on the MC22 wheel being able to fit, IIRC MC17 rear wheel fits if you use the NSR spacers and cush drive, MC19 rear wheel is a straight bolt-on on the MC17, and MC22 uses the same cush drive as all the previous bikes (but with different collars), so I'd say that the chance is not 0.

Now for the concerns. One of the concerns is the length of the link. The YZF-R1 link that I'm using is longer than the MC16 link (160mm vs 100mm approx. hole center to hole center) because of the angle and distance to the connecting point on the frame. On the R1, the mount is perpendicular to the frame and points straight down towards the ground, while MC16 has it parallel and pointing towards the rear. So I will need to find or create some shorter links, or I might try to shorten and re-tap the R1 lowering link that I have, since it's basically a tube with some eyes threaded in at either end.

Another one is the rear caliper support. The RS250 swingarm came from what I believe was an ND5 RS250, and it uses a torque arm rear brake mount similar to the R5K MC18, so there are no support mounts on the swingarm itself. I would love to run that style, but that would toss out all of the previous info about wheel mounting, and I would have to figure out an attachment point on the side of the frame. I think that the swingarm itself is strong enough to support the MC16-style mount that braces against the top of the swingarm while braking. I will just have to find a way to keep it in place.

That's basically the gist of where I am with the rear of the bike, now, for the front. Not much to say here, I think that I got the right non-standard bearings to mount the GSX-R1000 forks on the NSR frame, not sure about the seals and spacers, but I might have enough parts to put something together. I also got an MC22 front wheel and the non-standard bearings to put that on a GSX-R1000 axle, which will need some spacers to account for the wider forks and will need some custom brake mounts to fit dual 320mm Yamaha discs.

Side note, what parts are needed to convert the MC16 engine to an MC18 speedo drive? Is it just getting the MC18 cover, drive gearbox, and speedo? I know that I'm running 17-inch wheel on the rear, but IIRC MC21 uses the same parts, just has a different tooth count on the rear sprocket to make the speedo work.