I used a Cyclotricity 250w front kit but the regulations have changed, you can plug the 'pedal assistance' and 'power level' into mine but now you 'must' fit those parts to be legal whereas I just use a thumb throttle on both my Trike and Maz's Dawes cos they were built up before the changes. It's still a good kit though.
What size wheels has the Super Galaxy got, if it's 700c you'll be OK but they don't do a 27" version.
Oh and I'd get the biggest battery you can fit, probably a 'Rack Mount' one, both of ours have these and they're a 'double decker' rack so the battery fits into a slot and the top is flat to take panniers etc.