Yes I agree . That is what I observed and wrote about in reply #13. .........................Just looking for insight so I can understand better.
Looked through pictures and found the arms without the holes were primarily found in 65 4100's ( A and K code)
5F07K2818xx & 5F07A2706xx (one of Mike M cars) were a couple of the latest (Sept 64)I have without the hole except for one (pictures do not show the stamped numbers) example that was on Ebay described as a "new take" Non K code carb.
As for those having the hole.
- Earliest example I found was 5R09K2141xx - carb stamped C5OF J (It had been restored)
- 6R07A1590xx
- 6R07K2040xx
- 6S1050 (It had been restored), 6S1177, 6S2086, 6S1455
- one loose (off the car) C6 C and one loose C7ZF C
Have one here at the house will have to dig it out and update the report.
Will likely repost with pictures over in another thread in another section since this concerns not just Shelby's