1st, A sickle bar is hands down the best weapon for cutting around a pond. My pond has 2 tributaries and about 1/2 mile of shoreline. I can usually cut it in about 30 minutes or less (if the cutter is already hooked up).
$1500 would be OK if the thing was rebuilt with new knives and plates. I think a new 9' replacement knife bar is about $135 or so from JD.
The chain in the middle is to hook up to your drawbar. If I remember right, you need to extend the drawbar about 12-14" back past the PTO shaft and pin it.
I'm worried that it won't fit without some extensions or mods. Make sure it will fit before you buy it. I went and measured across the 2 lower pins that your arms will have to spread open 32" to install it and they will be spread about 28" once installed. You have enough HP. The thing doesn't weigh too much, maybe 400-500lbs (thats a guess). But it does take some strength to lift it as it has a big coil spring (like a big garage door) that helps lift it when connected to the chain.
I just rebuilt mine. Bought the tool($35) to remove the knives and peen in the new rivets. What a job. I think I replaced over 20 knives. The labor involved was sweat equity. I should have bought a new replacement bar with knives. I put in 9 new ledger plates. JD wants you to order 25 at a time and my dealer had 9. It all adds up. I guess it cost about $250 in parts to rebuild it including the tool. I had to buy some rock guards too.
The 9' footer is the way to go to reach out into the water without sticking your tractor. A 6' or 7' would not be long enough for me due to the edge of my pond being soft. I go slow because it gets clogged up with previously cut decaying stuff. I usually have to back up, raise it, and move forward to get past the "clump" of grass. However it is much better since I've rebuilt it. When you set up the knives over the ledger plates the bar is usually flat on the ground touching at the inner and outer shoes, but when it is hanging out in the water the knives don't all scrape over their ledger plates so you can't just cruise along like when cutting a hay crop.