Jr 50

Jason, I believe the wheelbase is 34". This is not gospel but I believe it to be in the ball park. I am not aware of a 2 speed kit for the bike but there may be one out there.
I purchase a KTM sx50 Jr. for my 7 yr. old this summer and it is a great performer. Words of advise though: Buy plenty of thread lock compound and an assortment of replacement bolts....it WILL rattle everything loose eventually. I have also made rubber insolators for all areas of attachment for the pipe. So far I have had the pipe body and a bracket rewelded and the bracket on his silencer broke off yesterday while ridding. The overall quality of the Japanese bikes is not present with the KTM but the performance level of the engine and suspension are considerably greater that that of the XR50, Jr50 or PW50 etc..:)

on the two speed thing it only has high gear right now
all you have to do is take the clutch cover off and there is a gear position arm
grind the notch biggerin the opposite direction hard to explain but simple to
see with clutch cover off

what year is your jr50? i have a '81 jr50 parts bike. let me know if you end up needing a frame. i don't doubt that they are all the same.