Fumblin,
The 41-49 235 and 41-53 216 heads all interchange. Chevy redesigned the 235 in 1950 so it uses a different head. So it sounds like your early 235 has a later head, or was possibly converted to a 14mm plug which I believe was possible by a competant machine shop. After '48, if you went to the Chevy dealer for a replacement head, you would get the later style. Or more than likely in your case, a trip to the boneyard to replace a cracked or damaged head would result in the swap. Like I said earlier, all 41-48 engines used the 10mm plugs.
The AC104 plugs you had were listed as original equipment on 41-48 trucks and sustained high speed use in passenger cars. They also had an M8 plug that was standard in passenger and for sustained low speed use in trucks,(aren't they all low speed)?
Hope this helps.
Bob
