For 1/2A stunt I use 3" bellcranks, slows the action down enough to pretty much eliminate the 1/2A "twitchies". I cut mine out of 3/32" ply. Use a very short pushrod arm and let the BC pivot as far as it will (mine are about 170 d.)--makes 'em handle much more like the larger planes.
For sport planes the nylon 1/2A bellcranks work fine. Speaking of that, I'm in need of a supply of those little one-bolt horns that come attached to those nylon bellcranks. I know a lot of guys just throw them away; if you could throw them my way I could sure use them!
Maybe I'll put a note in the "classifieds" section too...
--Ray