This is an odd arrangement. Why bother putting a front sight there, one with tritium insert at that, with no rear sight?
If you must have a ghost ring, Trijicon will sell you a TA01NSN
rear sight, you'll still need the lower part of an
RM38
By the time you get an RM38, you might as well get an RMR to go with it.
Back in 2000 or 2001, the only ACOG that could accommodate a red dot sight was the TA01NSN, and only the prototype KAC red dot sight mount existed and nobody could buy one. We made our own until others, including Trijicon (belatedly) produced better plastic Optima 2000 type or Docter sight mounts.
I don't really like the Trijicon RDS mount (not RM38, Trijicon didn't have the RMR back then, only the all plastic RDS, which is essentially an Optima 2000 sight I think, and the aluminum/glass Docter sight) on my TA31F, it doesn't seem very secure to me.
I much prefer the offset iron sights/RMR mount setup of the TA31ECOS, I don't think Triicon sell those separately.