OK, let us know how you get on. (As a new forum member your posts are currently subject to new user moderation / delay. After a few more posts that will wear off and you will be able to post in real time).
The connectors I currently have on my MK14 (rear edge and keypad connector) were bought around 2012 from RS, and are both exactly the right length, single sided with no keyway - it's almost as though they originally stocked them with the MK14 in mind and still had some stock left all that time later.
I'm not sure if they still do them now though, and even if they do, they were tremendously expensive 6-7 years ago, never mind now.
Edit: On a quick look, they still do the 32-way version - note that although it looks double sided in the illustration the upper and lower contacts are paired so there are only 32 pins sticking out of the rear of the connnector. Not so useful for those of you who have late issue MK14s which do have double sided rear edge connectors. Here they are - the keys in the outer ends (position 0 and 33) are removable.
https://uk.rs-online.com/web/p/edge-connectors/0466551
... but look at the price! They might even still do the 16 way one as well, I did not look that far.