I'd check out small drum mowers like these.
Mini Hay Balers and Compact Hay Balers | Small Farm Innovators
Something like the DM 3575 would get you a 6-ft cut with your JD 3520 CUT. Nice thing about drum mowiers is that they don't clog like sicklebars.
Drum mowers will produce fairly wide and flat windrows. If that's a problem, Galfre makes a drum mower with their built-in "Black Hole" conditioning system that spreads out the cuttings similar to a sicklebar without making a windrow.
Tractor Tools Direct | Galfre Compact Drum Mowers
BTW: a brush hog can be adjusted to chop the cuttings into mulch-like condition. To do this you set the front end of the mower 2-3 inches higher than the rear. That way the blades will slice through the cuttings several times before ejecting them out the side. It takes a little more pto horsepower so your ground speed will be lower in this mulch mode.
Good luck