HJM,
From my UL experiences in guitar amps, you get less power and a less lively top end - you don't get that crispness to the treble with UL. I honestly wouldn't bother mate.
I've got a HW-series Dagnall OT on its way to me for my main Simms Watts hotrod, should be interesting to see how the stock OT hangs in there with something decent.
:twisted: