On the driver's side cylinder head, next to the temperature sender there is a 3/8 threaded hole.
I know that hole has to be filled, but wonder what that hole is originally for?
It must have secured something?
Anyone know?
Thanks
Jim

The 3/8-16 threaded hole under the distributor holds the spark plug wire loom.  The opposite hole on the other head is typically used to fasten the ground strap from the firewall to the engine.  Both holes do need something in them to prevent oil from misting out of them. 

Lorena, Texas (South of Waco)

As I recall the bolt should be only long enough to plug the hole. It could interfere with a pushrod if too long.

Thanks Guys
I forgot about a ground strap being needed.
Thansk again
Jim