@“Rod Knox”
"Putting pressure directly on the rail itself, the rail in the tail piece that is, would seem the safest route if there is access to it."
Where is the rail in the tail piece? Is that the “tab” I was talking about, or something else?
@fillyblynn, looking at the most recent photo the R/OD rail appears to be somewhat visible there in the Reverse housing inside the blue circle, Further to the rear is the OD housing apparently under a seperate cover. Is there another cover on the tail piece? If so remove it and there will hopefully be access to a position where the rail can be pried or tapped to free things up.
To get at the 5th / reverse shift rail you basically have to take the rear of the transmission apart.
The following information is from the library edition of AlldataPro.com.
Remove the extension housing
Remove the VSS tone ring
Remove the counter shaft lock nut
Remove the counter shaft rearmost bearing and thrust washer
Remove the output shaft rear bearing lock nut
Remove the reverse idler shaft bolt
Remove the reverse idler shaft, gear and bushing
Remove the output shaft rearmost bearing
Remove the output shaft reverse gear and bushing
Remove output shaft gear spacer
Remove counter shaft reverse gear, 2 bearings, and reverse synchro/blocking ring
Remove reverse gear thrust washer
Remove counter shaft split washer
Remove 5th / reverse gear shift rail bolt
Remove 5th/reverse syncronizer, gear shift fork, and reverse gear shift rail as an assembly
Alternately you might try removing the 5th / reverse shift lever (the tab you have circled in blue). Remove the circlip ring; unbolt that shaft lock bolt; remove the shaft; and lift the lever away from the gear shift fork. Now you should be able to access the shift fork and clutch dog sleeve directly. See if a little prying is effective.
When you solve this problem let us know what the source of the problem was.