As was said above, the spring can be a bit of a pita to work with. It's been some time since I've torn into mine, but as I recall, I used a valve spring compressor to compress the spring for removal, although I've never tried this on a broken spring.
For installation, I carefully compress the spring in a device consisting of a bolt, nut and two very thick washers notched in 3 places about 120 degrees apart (to allow the wiring described below) until it's length is sufficiently compressed such that it will - upon reinstallation on the shift lever - allow the keeper to be slipped in place.
With the spring compressed on the nut-washer-and-bolt device, wire the spring (using double strands of good quality wire) end-to-end. The notches in the washers will ensure the wires are spaced about 120 degrees apart. After slowly unthreading the bolt and observing the spring remains compressed, just slip it over the shift lever, slip the keeper in place and cut and remove the wires. Although the spring is pushing on the wires, I've never had difficulty in removing them once cut.
If you have Volume 7 of "How To Restore Your Model A" there is a good article entitled "Transmission Shifting Tower Repair" by Les Andrews on pages 105-106 that shows a different spring compressor and, in any event, is worth reading before tearing into your tower.
There may be other approaches that are easier or have some other advantage and if so, I'm certain others will chime in with such. But for a one-off infrequent job, that's what worked for me.
