Somewhere in my vault is a 20 inch barrel marlin 39 .22 with gold trigger. I only keep it as training rifle for learning to use the lever action center fires. I keep a lever gun in 30-30 just for the time my semi-autos get outlawed at some unknown time in future when our government goes all UK and Australia over us.I believe the only difference between a 39D and a 39A is the D has a 20” barrel whereas the A has a 24” barrel.
The D was only made for a couple of years in the 70s.
Both are great guns. I’ve got a couple of 39As.
I wouldn’t sell mine for less than $600 but your circumstances may be different.