You should have no problem running a sickle bar mower with your tractor. It does not take much horse power. My dad has cut hay for around 50 years with a Farmall Super A with a 7' cutter bar. I think a Super A has less than 20 horse power.
Kuborta B2400, L2900, L4330; Caterpillar D3B, John Deere 455D
I have an old and very heavy John Deere 350 belt drive sickle mower, 9 foot bar, on a 24hp Kubota B2400 HST. The tractor has plenty of power. The biggest issue was the offset weight of the mower which the small category 1 three point hitch did not handle very well. I eventually built a sub-frame for it, similar to those for backhoes. If you get one of the newer and lighter five foot or seven foot mowers you may be okay.