According to my old 'Fix Your Chevrolet" book published 1963, the recommended plug for a 1958 235 six banger is an AC44 with a .035 gap. Same plug listed for the 265 and 283 V8.
They switched to the AC46 for the 1962 235.
Autolight 306 does seem to equate to AC46 on this site:
https://www.sparkplug-crossreference...rt/AC_DELCO/46