A wideband O2 sensor kit may help. You'll need to weld a bung into your exhaust and pay for a sensor box, but you can move it between cars if you want.
You'll want to have someone else drive and you can watch the readout, then go to your carb tuning book (I mentioned that too, right?) and modify your carb to be slightly lean at cruise and not too rich at idle or under acceleration. A little trial-and-error later and you have it set!
If you change carbs on your car, it's really the right way to do things. I'm saving up for one myself, and they keep getting cheaper.