Stem length?

I'm planning to use a regular Cinelli race bar. Turn it around an cut it.
It goes on a Motobecane from early 80s. I believe the size of the rame is 60.
And I'm 183cm with long arms... :-)

What's a "bar spin"?

I'm 198cm with a 61cm frame and a 12cm stem is too long for me by about 2 cm. And i have relativey long arms and torso.