The best way is to read your plugs or get a data logging wide band. FAST has a nice one for just over $400. It's portable so you can do a bunch of cars.
Here's a good page on plug reading on FBO's website.
http://www.4secondsflat.com/Spark_plug_reading.htmlMake sure your float level is set correctly. Also, did you shorten up the mechanical advance slots in the distributor? Slanty's like significantly more initial, but not more total ignition advance. The difference the distributor recurving makes in a slant is unbelievable. Are you still running points?
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