Hi Darryl,
I'm not sure but I think you've got the wrong end of the stick, its the 20 inch Electric unit that I would like to convert to petrol and I am getting a 18 inch petrol powered unit given to me on Thursday. I'm happy to sacrifice the 18 inch unit to get the 20 inch up to a good petrol powered unit opposed to it being electric.
Sorry if I've confused you, but regardless of that I'm thinking of I feel shaft lengths are going to be an issue as a 18 (Petrol) would have shorter units than a 20 inch (Electric). If it was the other way round it would be easier as shafts can always be shortened but lengthening them would not be that feasible.
Yes the Villiers is definitely not my weapon of choice, a good Chonda would work well with a 20 inch unit. Also sorry that I've called the smaller unit a 17inch in the previous post as I got it confused with it being a Model 17 that was only released in 14, 18, 20 and 24 inches.
Let me know what you're thinking Darryl.
Cheers,
BB