Hi Sam, The loss of one inch or so shouldn't affect the functionality
much.  I don't know your skill set but you can remove the mainspring,
anneal the last 2-1/2 to 3 inches, punch or drill a hole, bend the
inner end, and replace it into the barrel.  You don't want to re-harden
the last couple inches (2 to 2-1/2") as that portion needs to remain
pliable to wrap around the spindle.

My guess is that the spring barrel will have a slit in the side wall so
it is likely to be easier to remove the entire spring.  Straighten it
out as much as you can, anneal the last 2-1/2 to 3 inches and punch or
drill a hole.  Don't try to drill before annealing, as the hardened
spring will crack.  Bend the inner end into a fairly tight loop and
feed the spring in through the slit in the housing, from the outside,
by winding the key on the arbor.

Best of luck,

Don Caine - Proprietor, The Music Box Repair Center Unlimited
Lomita, California, USA
http://www.musicboxrepaircenter.com/ 
mbrcu@aol.com.geentroep [delete ".geentroep" to reply]