for the comments
I knew it was not easy but it got even worse
I knew I had to figure something out for the rear brake pump because the bolt holding the brake line would touch the swinger. At the moment I have put some spacers behind the footrest plate but I am going to turn the brake pump 1/4 round so the plate can be mounted in it's normal position and the swinger is cleared.
Of course you need spacers at the swing axle and at the rear wheel because I am using the B4's wheel and rear brake. You also need to weld a mounting position on the swinger for the brake caliper's torque link.
I was using a longer than stock rear shock (GSX-R 750 '02) which raised the bike. The swinger is shorter than stock so it raised the bike again, which was too much for good handling. I was also short of space because of the piggyback reservoir on the shock. The GSXR 750 '91 shock is much better because it is not longer than the B4's, resulting in a better ride height, and the reservoir can be mounted somewhere else. This is necessary as the swinger would bump into the coolant reservoir, so you need to raise it by using brackets.
The biggest problem is the swinger bumping into the tube on which the battery tray is mounted. Instead of 120 mm rear wheel travel I only have 100 mm. If you use a long shock and raise the bike some more with other dogbones you won't have this problem but you won't have good handling either. So the only solution (if you are persistent in keeping the RGV swinger) is to cut off the tube and weld it 40 mm's further to the back of the bike. This will raise it by at least 40 mm's (the angle of the subframe at that point is at least 45 degrees upwards) and clears the swinger.
Since I am about to spray the new front rim and front fender from a GSX-R 750 '92 I can respray that part of the frame after welding. Maybe I am going to use a RGV 250 rear wheel (wider rim which can hold a 160 tire) so I can remove the spacers there but that depends on the bike's geometry. Right now my front tire is at full lean while my rear tire is not, resulting in a sliding front. With a 120 front tire it might be the other way around or it might be just right.
To be continued