I got one that is supposed to be off of a 650. Its round and its an inch longer but the shock mounts are positioned closer towards the front than the 750 swingarm and a little higher. Looks like it ends up at the same spot compared to the 750. This might make the stock frame sit higher w/stock shocks. Prolly the same angle. I planned on using short shox so in my case the angle wont change much.
Most guys report the 650 is more than 1 inch longer, so I am suspecting that I have a 550 swingarm.
I would be interested in pics, but I do not think its a common swap. The round as opposed to the welded seam 750 looks better IMHO.

"We must all hang together, or assuredly we shall all hang separately." Ben Franklin at signing of Declaration of Independence or was it Dawg at the WHCM to the other HCMF's.