On my sf conversion, I put the motor in the frame and bolted it at the swingarm pivot and the bottom mounts. That should get the motor centered in the frame. I then measured each side and used my band saw to cut the swing arm a little larger. I then sanded it with a belt sander while frequently testing for fit. Once I had it fitting, I measured inside the swinarm to see how wide I needed my races. I wrapped them in tape until the tape was level with the flange and clamped them in a carbide cutoff saw. I also cut them a little longer and fine tuned with my belt sander. It didn't take more than a couple of hours to get it fitting really well.
