Which model sabre is it? If it's the 2048 garden tractor (not like the L series) it will probably be the same linkage kit which is required for the GT242/262. If your Sabre looks more like one of the home depot type lawn tractors, it probably won't work.
How much did you pay? they cost around $1400 new. If you can get it to work, it's a fantastic attachment. Go to the link below and type "tiller" in the equipment search, then scroll down to 2203 30" mechanical tiller. You'll see the three linkage kits offered. They cost around a hundred bucks. You won't find a used one on eBay unless it's attached to a tiller for sale.
Good luck.

Here is a link that might be useful: jd parts

my sabre looks like my other ones. i have 4 now that i've rebuilt. this is the biggest one at 20 hp. i have $125 in the tiller and $150 in the tractor. i repaired it's transmission/axle. so yea, i did good if i can find this linkage kit. i really only need the specialty clips and maybe a rod. i can make the rest.-dave

I actually have a slightly damaged rod (AM137355) and NOS arm (AM133353) for the GT225, but I don't think that is the one you need. The rod had part of the threaded end snapped off, I believe. Let me know if you're interested and I'll put them on eBay.
Sounds like you got a really good deal. Was it really new in the box or was that just a figure of speech? Must have been a big box!