Posted by NITRO on August 28, 1998 at 18:56:56:

All EGT probes, regardless of application should be installed at a location which would be 1/2 the primary tube diameter from the head surface. So if the ID of your primary tubes is 1.5", the hole or bung should be located .75" from the head side of the flange. You may place it at any angle to allow access to header bolts, etc.
This is a position that's considered a "standard" for location in the automotive world, and allows people to compare apples with apples.