Phono Protractor. Recommendations?

If you want the best, and have multiple arms, get the SMARTractor. 
If you want the best, and have one arm, get the Mint. 
If you want to throw away $20, get the Turntable Basics protractor. 

louisl,
Your spec is most likely 258 mm. Remove the arm and measure pivot spike to spindle center for the actual.

Mint

I have all 3, Mint, Dr. Feickert, and SMartractor. They are all good. I like Smartractor the best. If you plan to change cartridge more often, I recommend the Smartractor. 

get a 3D arm and the 2nd pivot.