From what I gleaned from the CAA G-INFO stuff, it would seem a bigger engine is fitted – G-SWOT has a Cont. O-200.

Another Super Wot, G-AVEY, has a Pobjoy fitted. http://www.devonstrut.co.uk/pages/gallery/superwot.html

Presumably there’ll be some beefing up of the structure to accomodate the larger powerplants?