Moorespeed has been into building race engines and has a very good reputation. I'd tend to believe the promo.
The HP isn't the important thing with a GS - it's the torque and it looks to have some real grunt.
There's a LOT of cool stuff about that bike - the conversion to monolever for one, although I don't know how they can provide the earlier 80 G/S rare-as-RHP (rocking horse poo) three bolt final drive and wheel. A lot of the weak areas have been addressed and handled well.
You're not looking at a cheap make-over - not at all!