The only problem, that I see, with a big engine on the stearman is vibration. My engine weight the same as a da50, and I am just moving the batts to correct the cg, that´s all. The stearman doesn´t feel heavy on the air, and the good thing is that with more power I can have same real fun or just slow down and make some scale type flying and have even more fun.
When I bought my stearman I installed a os 120 four stroker. The engine was at high throttle almost all the time and I wasn´t able to make all the maneuvers that the plane was capable of (Maybe my fault) but now with the bigger engine I found it a lot more fun to fly, and I don´t consider that is overpowered for what I like to do.