Thank you for joining the Intel communities.
In this case the operating system will work with 32bit only and Ubuntu can work with 64Bit you can see it here:
About the UEFI image let me find out for you to see where the UEFI image is located on the Intel® Compute Stick.
Well the fact is I think you do anyway, since it's available as so called BIOS updates on the download center.
Anyway I never expected any Intel staff to participate in this thread since you don't really have obligation to answer questions in the original post.
Also this thread is more about the location of the image and if, it sits in both of the two eMMC boot partitions, how is it splited. So what I want is more of some technical details of the stick rather than the getting the UEFI image itself. However, again, I never expected Intel to reveal it. I have only intended to seek answers from the community since it can be easily revealed by an ICS owner with Linux, though I never have high hope as well since I don't think many would bother about it.