Graham,
I've been making Mouse Race and 1/2A proto bellcranks out of 6061-T6 stock .032" thick. I use a standard AN470-AD3 rivet for the post or button. Use a double loop on the lines since there is no pulley, per AMA rules. I would have to check my notes, but I think I make the loops 5/8" long, and the diameter is about half the difference between the rivet shank diameter and the rivet head diameter. When you set the rivets, put a small spacer under the manufactured head while you set the shop head. You will probably have to cut the rivets to get the right length, and then I file the shop heads to eliminate any excess. No failures or issues to date. Sorry I don't know how to attach a photo.
You would have to beef this up considerably for a .15 sized racer or speed plane. On .15-.40 size racers I have been using the Fox 2" bellcrank in stock condition.
Dave "McSlow" Hull