Would it be 'wrong' to turn this rotrax into a fixed gear?

Oh and if you fancy the sugino 75 crankset I would have slapped on the rotrax, make me an offer. I guess it's a 9/10 - decals a little scuffed but 100% otherwise. 50t.

I might be into those cranks, if there open to anyone..

what length are they?

thanks