Well, there is a procedure to convert them to 1.75mm. It's on the reprap wiki, along with everything else you may have ever wondered about the J head. http://reprap.org/wiki/J_Head_Nozzle#1.75mm_Conversion Looks doable. The normal metal hollow-lock screws are fairly cheap from McMaster-Carr, as is the PTFE tubing. It looks like you shouldn't have to machine anything to get it done.
tmccafferty wrote:Looks like everybody is out of stock. Argh!
hotends.com seems to be pretty consistently in stock on Friday afternoons if you can wait.
But if it were me, I would probably just contact Reifsnyder and ask him exactly what I need to order from him to do the conversion. I imagine he would be happy to help.
Got the new extruders in the mail this evening. Ya...hoo! Got it installed and the resistor potting is drying. Hopefully will be squirting plastic by morning