Frank here's a photo of the reverse solenoid on our 4104s
When you put it in 1st gear and hold the reverse switch on the dash panel and simultaneously move the shifter into 2nd gear the activated solenoid would be moving the shift into reverse. Is your solenoid pulling like it should while moving from 1st to 2nd gear while simultaneously holding the reverse dash switch? If not check the wiring going to the solenoid. That is where I'd start. It could be other things like your linkage but best to start with the simple things, Notice the extended rod on the solenoid arm that extends beyond where the connecting pin to the solenoid pull plunger is, if there is no electromagnetic pull from the solenoid during reverse shift use the extended rod on the arm to manually push the solenoid forward by hand while shifting from 1st to 2nd. If the solenoid is the problem that will get you in reverse gear. HTH
