another answer to your hunting and too rich problem
I have built two 57's with 502s in them and have had the same problem of hunting and too rich and really lacking in power with both of them. One was a 3 and the last one is a 4 type. What I found on both of them is that the factory tightens the valves WAY too tight. I would suggest you adjust them if you haven't. You will find that you can back them up a full turn and still won't have any clearance. If you do it with the engine running get ready for a big mess of oil on everything. I actually read your post today looking for an answer to another problem that I am having with the type 4. I hope this helps. It will cure it!