Re: Terrible gas mileage,
 

I gonna pull a plug on each side and stick a spring hook down into the hole to see what's up. I have a set of short plugs in there now, but I found 2 boxes of the correct NGK plugs in my stash that are long reach.
When I pulled them the other day it seemed that they didn't screw down very far until they tightened up. Short plug in a long hole?

Re: Terrible gas mileage,
 

Here is what the different plug holes look like.

Re: Terrible gas mileage,
 

I have a 62 Owner's manual, it list the C44S plugs for the 305D, This number as old as it is most likely has been superseded with a different number. I would say you have the 3/8 reach plugs.

Re: Terrible gas mileage,
 

I also have the original owners manual in my glove box, just didn't think of checking it. The C44S was the plug listed in the Motors repair manual for the E model so looks we are narrowing it down.

During my searching ran across a great site for cross referencing sparks plugs, has cross to everyone and explains what all the numbers and letters mean.

http://www.sparkplugdepot.com/cross

thanks guys,

gg

Re: Terrible gas mileage,
 

Gents, a D engine would have ended production in '62. The .375"/.750" plug length problem ended in '63 with the appearance of the E engine. The picture you posted jagarra is a set of heads with the .750" reach plugs. The original AC plug for that engine was the 44NS non-resister plug. AC superseded all N style plugs with the XLS style plug. I picked up 2 sets of C44NS plugs on evil-bay several years ago. I like the "C" plugs because of the thicker electrodes these plugs have. The C plugs were originally the "commercial" version of the plugs the light duty engines use. The reach controversy arose because early engines were burning up plugs and cracking the heads around the plug port due to casting thinness. The .750" reach heads is the correction of this problem.