Re: Fender Pro Junior Amp Mods?
IIRC the Pro Jr has been modded to 18W style circuits, and there's probably info on 18watt.com.
The Blues Jr has 3 preamp tubes which means you can do a fairly faithful 1987/1959 circuit. You may need to make the board yourself or find someone who will make one. Edit: and, of course, a new faceplate which can be done by your local trophy/ engraving shop.