I have a complete guide of how to do the 4k dizzy setup. There is a Bloke in the states doing a "swap over" for around $300US.
Basically involves making up two spacers, one for the body and one for the shaft.
And cutting off the 4a gear and welding it onto the 4k shaft in the right spot.
there is also a bit of effort involved in the mounting/adjustment part of the dizzy.
The other way is just to use a regular 4a dizzy, and a standalone ign. controller that has a built in curve.