I was exactly in the same position as you. 2 blade mac on my eagle. They won't sell you the STC, however if you buy the screaming eagle conversion, AKA the O3 310HP conversion, the STC for the Prop is in that so you wouldn't need one for the prop on top of the 310hp conversion. I was originally between buying a brand new acclaim Type S prop (7498) without the 310hp STC, or the Ovation prop (7693) used without an STC and get the O3 conversion.
In the end, I took the 310HP with the used prop since on my eagle it gave me a 70hp boost, a 170 pound gross weight increase, and significantly better takeoff and climb performance, and it ended up being the cheaper option. In your case, if you go the 310hp with the used prop it'll give you a 30hp boost, and significantly better climb and takeoff performance. If you take the Acclaim Type S prop, it'll be probably a bit better cruise speed, a little better climb performance, and a little better takeoff distance.
Shoot me a PM or give me a call and I'll guide you through the process in order to do the used prop route.
I will say the 310HP is a completely different animal. With just myself, and 35 gallons, Takeoff roll is about 600 to 700ft, initial climb was +2000ft on a mid temperature day climbing out at 105 knots for fun at sea level