I don't see the connection with the 60 warbird. In any case, WM planes fly best at spec and the T-34 is no different. I have several planes from WM and each time I have been a little too aggressive with the power! However, after flying so long, I think the right engine with the right airframe is still the sweetest combination.

If you really want to reuse the engine with a warbird (probably not 60 size, though) you should get a 4-stroke. Something like a a magnum/asp 61 is just right. I have one on a scale cessna and it's a beauty with a wonderful sound. It won't go vertical by any means (8lb plane) but it is great for a budget, sweet sounding plane. If you have a little more budget, you can go for the Y.S. FZ63, a Saito 76 is sweet or something like an O.S. ultimate 70. Of course all these will mean that you will have to get a 40-46 size warbird instead.

If you oversize the engine, you can expect that it won't fly well as a second plane. If you're going from an avistar, stay within the range.

I forgot the obvious choice. Just strip your avistar for now, fly the WM until you're comfortable with it. Then when you think you can move up to a warbird, stick a 4-stroke TT 90 or Magnum/ASP 90 on the T-34, balance it and fly it. You will get a feel for what the Warbird's wing loading is like. Personally, I think this is the best choice. Of course, if you don't like the TT or Mag/ASP, you can always go to an O.S., Y.S. or Saito 100.