You have 2 things working against you - non-standard lift arms, and non-standard pto shaft.
Also this tractor appears to have a very low pto - most tractors have the opposite problem, where the shaft compresses as you raise the implement, goes to max extention when you have the implement totally lowered. You will have the opposite problem, which is what is confusing some folks.
You mention you have 'the longest' lower arms, so I spuspect you are not at the 'right' length. Changing the bottom can have unexpected results - your 3pt now lifts higher which is heck on pto shafts. It also changes the geometry of the upper arm, which creates the bad angle (the tiller is hangine down in back) that we see in the picture. This is your biggest issue.
You have to do what you have to do to make the tiller raise level, parallel to the ground, at all times. A new upper arm is probably the cheapest, you should be able to find a shorter one. This will be perhaps the easiest fix, so I would really persue this - might need to order a top link if nothing local from Valu-Bilt or the like. With your tractor you will run into this issue again, might as well be prepared.
You really need to limit how high the tiller raises. My 1720NH came with the 3pt arms in the top hole, so it raised very high. Niffty! Until I put the snow blower on it, then it raised so high the pto knuckles clattered. No good. (My snow blower was already modified, see below.) The vertical arms that hold the 3pt on my tractor have 3 holes, and I had to lower it a hole. Your 3pt seems to lift from the bottom, not pull up with rods, so don't know how you adjust this?
I used to have my snow blower on a bigger tractor. I could not make the pto work - angle too steep when lowered, and as I pulled the 3pt up, the pto shaft would compress until it hit. Just no room for any workable adjustment on the top link.
So, I had some stiff strap iron straps cut & drilled, bolted them on to my snow blower where the pins bolted on, and this extened my lower links on the blower - which is where the real problem was. Only added about 2" (moved the pins on my blower 2" farther out), but made a world of difference.
I could get some pics if this is clear as mud, but I'm kinda infrequent here so you better PM me as a reminder....
--->Paul