Okay Mark.....I've found the difference. When they went from the MRK X (your 1986 catalog) to the 1010 (1990 catalog), the lengths changed. The MRK X kit has an 8" main BT (I measured it twice to make sure it wasn't 9") and a 4" payload BT. The tube fins are also shorter in the MRK X kit, 4.25" as compared to 5" in the 1010 kit.

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Don
NAR 53455
"Carpe Diem"