The problem with the aluminium wir is that it really brittle after time. Got the same shit in my house and replaced them completely by copper. That’s not the solution for every one so. Deepening on the diameter I would chose the right fuse. Fun fact it depends on load, wire diameter, wire length and the way of installation including temperature. Quite complex thing if u want to do it the safe way. If the wires are that old I would use a fuse already smaller than the aluminium wire is rated under the conditions I mentioned. If u want some help with that just pm me and I can explain how to calculate that stuff. Did that for 3 years of my life 🤣🤣🤣 just calculating circuits