What is wrong with a roll pin? They are sold by PartsMike for this purpose I believe. Just two roll pins for $5. If it works, it works.
If poster can find a kit or original Pins. Good.

If not: http://www.partsmike.com/index.php/products/623-024-sm420465-shift-lever-pin

Here are the dimensions for lathe made. They are stepped. Dimensions will also help in determining the roll pin size if desired.

Overall length - .715 to .720
smaller diameter barrel length - .523 to .527
Larger diameter barrel length - .183 to .185
Smaller barrel diameter - .247 to .250
Larger barrel diameter - .308 to .310

Everyone need to keep in mine that the sm420 is sloppy/large pattern almost from day 1.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn