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Hello and good morning RW,
The majority of sickle bars are now rear mounted on the three point hitch and you would have trouble reaching as you would still expose yourself to a roll over condition.
With your mowing needs you really need a rear mounted boom mounted Orchard and Vineyard Flail Mower shredder with hammer knives.
You have enough mowing work to justify a boom mounted orchard and Vineyard flail mower shredder with hammer knives.
You need loaded tires and suitcase weights for the front of the mule you have to manage a three point hitch boom mounted Orchard and Vineyard Flail Mower Shredder.
The Del Morino T62 boom mounted flail mower offered by Everything Attachments would be a good fit for your mule to do the mowing you have to do.
All you would need to do is have the tires loaded and invest in suitcase weights for good balance and stability on the shoulder of the road while you mow.
The other thing you obviously need is a tilt meter to prevent you from mowing on too steep a grade as the safest slope you should be mowing across is a 15 degree slope at a maximum angle.
If you go to the Bing web site and type in Del Morino flail mower a video will come up showing the T 62 boom mounted flail mower for you to watch.
www.Mascio.com.us offers a rear mounted sickle bar mower that is also almost 8 feet wide in cut that is adjustable to allow the user to move the sickle bar mower further to the right to mow a wider swath up and down banks. You would want a Mascio sickle bar that is designed for stony filed mowing with replaceable teeth. The Maschio sicklebar mower is made for cutting hay has many more parts and requires more maintenance so keep that in mind.
The Maschio folks also offer a three point hitch mounted boom mounted flail mower in their smallest models that would work for you being the Rosa with a 10 foot working width and the Margherita with a 12 foot working width. With either of these models of boom mounted flail mowers you would have to make several passes to mow to the full width of 10 or 12 feet in width.
You can watch them work on the Mascio youtube channel and I think you will be very impressed with their mowing ability and either model will allow you to quickly remove them and install other implements on the three point hitch.
Here is a link to their flail mower page.
www.maschio.com/catalog/catergory/bracci-decespugliatori/en-us