you'd need new transformers which will run you around $400. so if you change them make sure you get some real high quality ones.
I've been thinking of possibly doing a 2xKT88 100 watter. IMO the KT88 tubes have a much better bass response. It doesnt get "farty" or "flabby"just nice and smooth like you would expect from a bass amp, while still retaining the other pleasurable qualities of the 6L6 sound. and you wouldnt need to wire in the extra sockets
I like the sound of that non-farty bass with a 100 watts. Do the KT88's entail something more than a rebias?