The A2 should come annealed from your supplier, unless it is being resurrected from some other life history, then I'd at least check it with a file. If a file struggles to cut it, it must be harder than 48Rc, send it out for annealing.
Machining it, I'd consider using a short corncob rougher and hog cut steps over the arc, then finish with a stout radius mill.......lights out if need be.
Look at the feeds and speed cutting data. For the life of me, I cannot comprehend why they wouldn't have a multi-flute cutter. Single flute index on steel? That sounds bizarre!
A2 Data sheet