I don't know if this helps, but our 773 is almost 66" across the tires. Cheers - SR
 
It depends upon the rims. Bobcat offers rims with different back spacing.
When I looked at my 763C, the dealer had the inset rims installed. The tires were close to rubbing on the main frame. The previous owner was using it for snow removal and I suspect liked it that way for sidewalks and such.
A friend told me to get the standard rims. Increases side hill stability and you can install Over The Tire Tracks without adding spacers.
With the standard rims mine is just under 66" wide. I have about 9" of space from the inside of the tire to the main frame.
The narrowest you could possibly get is about 58". Which is about the distance from head to head of the axle bolts. With those inset rims the tire track was narrower, but the bolts stuck out beyond the rims.