the AFR spec for the 205s is Autolite 3922. I have the 205s on a sbf (dart block) 427ci making 560t @ 4400 rpm and 563hp @ 6500 rpm. We pulled the plugs on the dyno at each run, carb adj.... they were perfect color on the electrod. My eng builder, Brent @ B2motorsports, put in what AFR said to use... his point was, AFR did all the testing, could pick any plug they wanted and we just did the dyno.. why change??? I use the MSD ignition, gap = .044
Mark
copy paste from AFR
http://www.airflowresearch.com/sbf_install.php
Spark Plugs:
Use 14mm x 3/4" reach gasketed spark plugs, no tapered seat plugs. Street application use Autolite 3924, for 205cc & 225cc race head use Autolite 3922, or equivalent. Plug selection is of course dictated by many factors including RPM level, compression ratio, and fuel type. Forced induction or nitrous applications usually require 1 to 2 heat ranges colder. Spark plug gap should be determined by the ignition manufacturer.