Its no real issue, changing the gearbox sprocket - as I think that you will probably settle upon the 15T over 58T as a really good compromise. It isn't going to pull the side of a house down but with the B175 engine you might be surprised at what it will get up and over. 

I would recommend taking the L/H side covers off ( you will need to do this anyway to fit the bones CDI system) and stripping out the alternator etc to come at the sprocket - its a lot easier to do it that way and you can also clean the clutch actuation mechanism, check the oil seal and give it all a good lube for peace of mind whilst you are in there. 

It is possible to wiggle the sprocket out without stripping it all down but I find it takes longer anyway. 

Sponge