Dude, you really need to go 24v if you are after power per £ and its really that simple. Theres no need to go the Swaymar route these days as i done that in the 80's to my Tina, and as good as it was it was no match for what is available these days.
Just think, 200 horses just by a simple engine swap.
Over what you have already, i'd say its a no brainer dude
Get it done already