What kind are you talking about? Side shift or boom style?
Ain't no way an optimal sized boom style is going to work on a L series. Maybe a small 26 incher... but that is practically useless.
Some of the county and town mowers that run boom flail mowers are insane. Makes me question why they need such a large machine... especially when I was a kid, they used to use a sickle bar mower on a beat up John Deer open cab. Now they need to be air conditioned, heated, radios, etc. They probably got GPS in them and a laptop. Ahh, wait... it's just people's tax dollars... who cares about that....
Side shifts will be OK, but it limits what you can do with it if you want to mow ditches and banks.
Last thing you want to do is roll your machine...
Also price... a boom style is going to be some serious cash.
As far as turning it, my little
BX2200 lifts and turns a ~650#
Woodmaxx 62" flail just fine. I even tested it in heavy brush with the rear door closed to optimize mulching... no issues and no complaints. Did a great job and didn't flinch one bit. Mind you, at the end of the day, the engine in a
BX2200 is 22HP, after the HST to the PTO it's maybe 15-16hp on a good day. So I can only imagine an
L3901 or a
L4701... it'd be like a little toy back there.