Mike,
I also tried the edge sm from Cambridge, it didn`t fit and had the wrong pinion and wrong offset, i found them useless to deal with and they also told me that they supplied caterham which i do not beleive. I Fitted a trent unit in the end it works a treat. CC are currently selling a 1kw Bosch series wound starter motor which is very powerfull and should do the job nicely.
Rob