Yeah twisted heater wires reduce hum ,the magnetic fields tend to cancel. Its definately worth a try ,you could start with the input valve and work back towards the output stage, just do one valve at a time and see if theres a difference . Its most likely to improve matters on the early stages less so towards the output tubes. If you scroll down on the LAB page and find Anthons 5e3 post ,theres a pic of how he's done the heaters , you loop the wires up and away from the tube sockets .
One other thing , make sure your heater winding has a center tap connected to ground or else a humdinger pot (100 ohm) with the wiper to grounded, on the different Ampeg schematics I have they use either of those two schemes .
One other thing , make sure your heater winding has a center tap connected to ground or else a humdinger pot (100 ohm) with the wiper to grounded, on the different Ampeg schematics I have they use either of those two schemes .