4 Speed Shifter Not Catching Reverse

I've got my A833 on the bench with shifter and rods attached. I can shift through 1-2-3-4 normally, but I can't seem to catch the reverse lever.

I had the shifter apart to clean it up and re-grease it. At the same time I removed the bayonet receiver and swapped in a bolt on. The reverse detent spring is in place and I put it back together just as it came out.

What am I missing?

Thanks
So here's something to try.. I had the same exact problem when I rebuilt my 4-speed I had it in the car and for whatever reason it just would not shift into reverse. I think it was triple R or somebody you told me to loosen the side cover bolts just barely and push up on it and like really hard. I can almost remember maybe getting the Jack underneath the cover with a little wedge enforcing it up and then free tightening the bolts. Presto reverse worked fine... it was just that little bit of clearance that it needed for whatever reason inside...