Thanks, I checked out your link. That is in fact the fixture I have. I appreciate the efforts you have made and the time you have taken to try and help me.
Am I correct in thinking that it may be used on a number of barreled receivers and not just the '03? (just curious)

If I seem dense or slow to understand your answer, I need to point out that referencing other mount manufacturers and simply saying they are the same does not provide me the actual dim I was looking for.
The fact is that Forester has showed me their drawing of the over-arm and the hole to hole center distance between the two closer bushings is 0.500" (which is for the block for the barrel) on the over-arm (Forester's name for it), yet everyone of the blocks I have bought recently and in the past years measure 0.560". It has caused me no few difficulties. I have had to drill and tap the first hole, then move the Over-Arm 0.06" for the second hole in order to achieve the 0.560" hole distance between the mount hole centers on the barrel needed for the blocks I have. I drill 7.2" distant from the receiver ring block (distance between the centers of each block).

I cant remember who I sourced the blocks from years ago, but the most recent were sourced from Steve Earle Products and are listed as O & E blocks for the '03 rifle.
scope blocks (sorry, I was unable to make this an active link).
I have a number of sets of these blocks bought over the past 15 years from more than one vendor and the center to center mount hole distance of the short/tall barrel blocks are all 0.560".

I am sorry if my initial post may have been confusing, but if you re-read my initial post, I made no mention of the receiver ring and clearly stated (or so I thought) that I was asking about the block for the barrel.

You never mention O & E blocks, so I got confused and didnt understand your references to Redfield, Burris, Leupold modern base. However, may I assume from your replies that Redfield, Burris and Leupold make or made O&E or similar bases? (I am going to google them in a moment) For the record, I have tried to get my answer about this hole center dim from the internet with no success.

If the name O&E is specific to only one manufacturer (Unertl?) and they are called something else by others? I am simply unaware as it is one of many areas I am still learning to know.