A set of plunger crankcases wouldn't be very expensive then most of the internals are the same. Similarly you will pay less for a plunger gearbox than a swinging arm type. To be honest I can't see the point of putting anything other than a plunger engine in a plunger frame unless you do something exotic like a Kawasaki Z1... Regarding the wheel, I'm not sure about that, providing you can line the rim behind the front wheel and get the sprocket to line up as well you could be in business but I think you'd need to try the parts in a dry run before committing.