Ditto that. If you can't get reverse no matter where you put the lever, it is not a problem with the cable adjustment, assuming your cable is not broken or such. When you pull the column lever forward, you keep it off the detents so you have infinite adjustment.
Losing reverse is a common problem. That happened on the 413 Torqueflite tranny in my 96 Voyager, which is almost identical to a 727. I swapped in a used tranny because mine had a cracked case from a prior accident. In a forensic tear-down, I found the problem was a torn servo piston seal, which I could have fixed easily from the bottom with the tranny in the car. I think you don't even have to pull the valve body off. The 727 has a common problem where the L/R servo piston cocks in the bore. There is an after-market aluminum piston to fix that and costs only ~$12. A search should find it. That could well be your problem. Any tranny shop should be able to easily install it, or you could if you invest in a pair of long snap-ring pliers (I use a cheap set from Harbor Freight). Finding a shop that won't try to upsell you is the hardest part. Since tearing down my A-413, I decided I could rebuild a tranny myself, which I did when the used one later died (a shoddy rebuild, I found) then rebuilt a 4-spd A-606, which was even easier. I will do my 904's and 727 when they need it. I don't trust shops. I asked an Aamco shop in Atlanta about rebuilding a 727 I had out of the car, and they said they couldn't rebuild tranny's. What the heck do they do then? I had Cottman rebuild it, but didn't fix the problem, so maybe they just charged me a lot to clean it off a bit.