I need to replace #4 aluminum conductor with copper wire for my furnace. There are 60 amp fuses in the disconnect box at the furnace and the length of wire needed is four feet. What wire size will I need?

You will need 6 wire for 60 amp, you have 2 separate 60 amp breakers? Or just 1?

I have two 60 amp fuses in the disconnect box by the furnace. Code here in Panama City FL calls for copper and I guessed right. I purchased #6 wire with a #10 wire ground length of romex. I also found that I have #4 aluminum wire from my power box all the way to the disconnect by the furnace. Will I need to replace that with copper to get into code requirements? The run from the power box to the disconnect at the furnace is about 80 feet. Thanks for your help!