No such stuff comes up for
B&H #: APIMMNE927K; Apple #: ZOTP-MNE927-NK.
I was going to just leave it at that and move on as I'd already ordered mine from Apple directly; I'd hate to provide wrong info for folks here, so I went there to investigate.
What I found is that no, there is no peripherals configuration options for main imac product configuration pages, confirming what I wrote. See the link I provided above.
But one can indeed choose key w/ numeric, just have to work harder to filter it due to the wonky and less-than-optimal B&H's website. To do this, one will need to use left column filter (starting from main imac page,
https://www.bhphotovideo.com/c/buy/iMac/ci/6490/N/4110474295 ), to filter out the spec he/she wants, screen size, CPU, storage, etc, then you may see the options that way. Still not clear but you should be able to tell because you should end up with only two options, the same spec only separated by $30 difference. JD could've provided a clearer method for this, but there you go, folks.
For US folks who don't mind mouse but really want the numeric key, B&H is an option then. They can choose that or just go with the default key and save $75 further by choosing Adorama.
http://prices.appleinsider.com/27-imac-retina-5k-display-mid-2017
Keep in mind that, ordering from authorized resellers, will result in much slower delivery on popular options like 512GB SSD. It's probably close to a month or longer compare to 10-14 days from Apple directly (estimate they give you is 2-3 weeks now, but it gets shipped faster). But for some folks, that may be worth saving tax.