So what's the difference between a fusible link and an inline fuse of the same gauge?
Fusible links are rated by the gauge wire they are made of. Fuses are rated in amps.
I looked, there is really no definitive cross-over from link size to amperage. But suffice to say, fusible links are very tough and can handle a lot of current before they burn in two. A fuse is quicker and more susceptible to blowing.
The fusible link in this circuit is 20 gauge, which is very small. Thus my estimate that a 30 amp fuse would hold it, since the wiring in the circuit is 16 gauge wire.
Most other fusible links are larger, and if a fuse was to be substituted for them, it would have to be a large maxi fuse. As an example, in 1986 the fusible link for most of the electrical system and the alternator is a 14 gauge link. Since most of these trucks had a 100 amp alternator originally, you can see to substitute a fuse for the 14 gauge link, you would most likely need at least a 125 amp maxi fuse to hold that circuit.