I have an Ultracraft which i'm thinking of selling. No counterweight (I made a makeshift one and haven't got around to finding someone with a lathe to make a nice one).
If you do decide on selling please let me know.
If it's to go on a Rega it may not be ideal. I had it on a Planar 2 and I had to extend the legs so the bottom of the arm would clear (they used a very deep nut for some odd reason).
There is a very mint EPA500 tonearm on sale here that will be a "giant killer" on that SP10 ....
Whats your budget