I'm guessing that you don't already have the 95 swingarm, or you wouldn't be asking if it will work. Have you considered cutting your 98 swingarm down? I had to cut mine down to fit the 500 in my 03 250 frame. I cut mine with bandsaw (although I have seen people use woodworking saws with a carbide blade) a little large and then use a belt sander to fine tune the fit. I just put the motor in the frame with the swingarm bolt and motor mounts installed, measured what I needed on each side and then repeatedly test fit the swingarm as I sanded until it fit. It took me about an hour total. You will need to put new bearings in the swingarm, and to cut down the races. For the races, I put tape on the until they would sit flat in the cut off saw and then cut them. If you don't put the tape, they won't sit flat or cut straight.
If you still want to try the 95 swingarm, I would just buy a cheap one and give it a try. You may be the first person to try this, and can educate the rest of us of if it works or not. Worst case you could always re-sell it on eBay.
