Been there... Canada's winters are so unkind. It's been a while, but the last one I broke was on a 78 245. Replacement involved removing the driveshaft from the tranny tailshaft, and dropping the tranny crossmember (get a jack under it first! It's supporting a bit of weight...) so that the back of the head rested against the firewall. You might want to remove the set screw securing the shifter pin (base of the shift lever, where it meets the shift rod), then drive that pin out, before doing this. I believe it's a 4mm allen screw. Use a good quality allen wrench, the type that is designed for use on a 3/8 ratchet, and put a bunch of extensions on it then hammer it soundly into the head of the screw before trying to turn it. 18 years of salt will not have had a positive effect on the threads. The 3/8 drive allen keys are available at Canadian Tire for about $6-$8 (Mastercraft, lifetime warranty), last time I had to buy one. And although they're not Snap-On, I haven't broken one yet.
Good luck!

-Chris