See if this makes sense,
If you have something like a TA01, which does not have the BUIS (backup iron sights), you are going to need to order two items:
135-TA: This is the top piece that will hold the JPoint
135-TAS: This is the bottom piece that will attach to the top piece and from a ring around the ACOG body
If you have a TA01NSN, which does have the BUIS, you will only need to order 1 item:
135-TA: This is the top piece that will hold the JPoint, and will replace the existing rear part of the BUIS. This will connect directly to the ACOG body so you will not need the second part.
(The pic above is to show how the top part can mount directly to a NSN ACOG body, ignore the fact that it does not have the protective side wings.)
If you have not already talked to Grant, definitely get in touch with him. He can walk you through everything, and he can also supply the items that you will need.
Good Luck,
Capt Richardson