Hi James,
Welcome to the forum.
The only one used from the factory that I know of is the 1 1/4" version.
Perhaps others will chime in but I supect the answer you will get is that anything may have been swapped in over the years from military or civilian life but a 1 1/8" shaft is not the common version.
Are you measuring the shaft here? (The shaft in the picture is 1 1/8")
A good source for info on Dana 18's is at novak conversions website:
http://www.novak-adapt.com/knowledge/model_18.htm
If you have any questions specific to your jeep I may be able to help as I currently have CFR 67-07809 from CFB Chilliwack and I live near there.
P.S. Contact me via PM if you are interested in obtaining (trades are best) another Dana 18 that was pulled from my other '67 CDN2.