I was able to just squeeze the frame in the sand blasting cabinet with about an inch to spare.
4 hours later of awkward turning and blinded by sand, the frame cleaned up quite nice.
After reassembly I noticed a problem. The rear wheel is not centered in the frame. But the chain was definitely in line with the motor when it was together. After doing some research I figured out the problem.
The rear wheel is not meant for the spacing of this this frame. The wheels are from a GR650 which has a wider swing arm.
The GR650 hubs and the GS550 hubs are the same except for the actual width of the hub.
Why am I going through this do you ask? because the GR650 is a 16" rim and I already bought these tires. I dont want to run a stock GS550 18" wheel on the back.
More updates to come.