I think I fried my amp gauge!

No dammit fix the problem FIRST. Or at least troubleshoot the problem so that you understand it fully

Swapping the alt/ battery wires, if you are talking about the large supply wires, should cause no problems except cause the ammeter to read backwards. That unless you "arced" (shorted) the battery to ground, and put a great deal of current through the ammeter. The most probable failure is the fuse link

It IS possible, however for the ammeter to fail. Only one way to find out....................pull the cluster

Not familiar with the access/ room under the dash on those old girls. If you can reach the ammeter terminals, you might (AFTER DISCONNECTING THE BATTERY!!) remove the ammeter wires and or jumper them.