I don't know how much help I can be. The total length of mine doesn't seem to fit any of the catalogue descriptions available. Ninefinger is missing 1988 and 1993 catalogues. Total length is 53". Every other year is 50" for the Phantom 4000 and 50", 62" and 56" for the 4000HD. Mine does have TTW fins with 1.5"mm which fits for the HD other than the length. In the '94 catalogue it also lists the 4000 with TTW fins so I have no idea. The fella I bought it from said it came with a launch kit so that tells me it's just a 4000. I have no clue.
The measurements are Total Length 53", BT is 34" x 4" and Fin root is 8.5".
Here's the Ninefinger link
https://www.ninfinger.org/rockets/NCRcats.html
For the 2600 it lists 30.5" total length and 2.6" for '86 but goes to 2.7" in '87. From 1989 -91 it shows 32.5 total lenght and a BT of 2.7" and does not list the 2600 for 92 & 94.
You may be able to narrow it down if you can find the right nose cone in their catalogues.
Good luck.