IMHO there is nothing more important than upgrading the high current stuff in your Datsun, including those fusible links with some new items.
Nothing goes to hell faster and leaves you dead on the side of the road than a dirty connection flowing 30+ amps.
There are literally hundreds of MAXI, MIDI and other fuse options out there including breakers, which you never have to find a replacement for in a pinch.
Blue Sea is one of my favorites, as most of their stuff is high grade SS intended for marine service.
Little fuse/Bussman also have great high current breakers like this in amperage's from 50 to 200A. I swear they even one that has two breakers in one package....
I just posted this morning about a battery mounted fuse panel that might interest you as well.