No reverse after getting transmission back from the shop...

Hello, I am having a little conundrum..... I have a 1983 Mitsubishi mighty max 4wd that has had the powertrain swapped to a 2.0 4spd out of another 1983 mighty max. I just bought this truck knowing it had transmission issues ( stuck in first gear) So I pulled it out and took it to a shop. Now it has 4 forward gears. But no reverse. The guy I took it to said I need to get a whole new shifter. Of course I cant find one anywhere for sale. The guy said the gears are fine everything on the inside is there and good to go. so theoretically it should just go into reverse! but no such luck. When I press down on the shifter and move it to reverse it doesn't feel like it is locking into the gear. I know a little about transmissions like this but not a lot. I've adjusted the clutch and that is fine. So I am kind of at a loss. Where should I look to see what is stopping it from shifting into reverse? I apologize for the long post. thank you for any help.

Also, what other shifter assemblies can I use?? I have the 4 bolt plate on mine. Does the shift assembly from a nv1500 work? thanks again.

The issue obviously isn't the transmission or the shifter lever - it's the selector rods. Somewhere the selector rod and fork for reverse has dropped out. The transmission shop should've been able rectify this without having to pull the entire transmission apart. Does the shifter lever feel like it just drops into the reverse position and loses any feel or tension on the shifter?

exactly geezer101, it goes into the position but does not feel like its locking into the gear. He told me I needed a new shifter,, sounds like I got told a tall tale....

it doesn't even feel like its trying to grab the gear at all....no clunk or grinding when I try to shift into reverse.