Yep, sounds like you grounded the main power circuit coming into the interior from the battery; i.e., you shorted your battery to ground. The fusible link is there to protect for this type of severe short. With that severe short, it likley went pretty fast. Inpsect the big red wire for any signs of melting at the cluster and all along its length to the firewall connector too. If none, you got lucky.
For the 60A altenrator I would not worry too much about the fusible link size. If the car is driven regularly and the battery stays charged the only real current back through there is the battery charging current which can be heavy if the battery is at low charge but typically won't be any more than before. And the orignal fusible link wil just protect you better; I would only mess with it if it started blowing in normal operation.
The main thing you need to worry about with the bigger alternator is the overall wiring into the compartment. Have you been pointed to the Mad Electrical mods for these cars?
I would buy a REAL fusible link, not fab one from regular wire. Fusible link wire is specific to the use. Try at NAPA. Use their online seaach and put in "No Vehicle Specified" and then search for "Fusible Link"