I've been trying to figure this out for awhile now, but it's hard to find much info. I own an AR XA-91 that my Dad bought brand new in '71ish, and passed along to me. It's awesome, and it's...exactly the same as the AR XAs I've seen online. Visually, I can't see any difference between the XA and the XA-91. Does anyone know what the actual difference is? Anyone who has more info on the XA-91 in general please post it here too! I'm always curious to learn more about this thing. It's still bone stock, taken out of the box a couple months ago after sitting in storage for nearly 30 years, and it sounds fantastic!