1946 Mercury Gear box stuck in 3rd Gear.

[Phil Gillespie]

This is a RHD car Column change 3 speed gearbox. Never had any problems previously.
Came up to an intersection went to change down from 3rd gear to 2nd gear and unable to get out of 3rd gear down to 2nd gear!! Not too far from home so got it home using 3rd gear only into shed. Will disengage with clutch.
Remove levers from side shifter to check. Front lever is 2nd /3rd rear lever is 1st/Reverse. There appears to be some movement in way of steel pin at shifting lever. Thought with only the levers at side of gearbox to move I could get it back to neutral. No joy. Only a small movement possible.
Can I remove the gearbox side shift cover to perhaps try to get gears back to neutral this way? Have done this with a 39 top loader.
This is my first with this side lever gearbox.
All advice will be greatly appreciated.
RHD car looking at side of gearbox with operating levers. Front one is 2nd/3rd rear is 1st/reverse.
Tell me it can be done this way without removing gearbox Hope Hope.
Phil NZ