Need a resource which would give the correct pin mappings

I need to connect about 24 signals (give or take, depending on how many pins to dedicate to ground and power) between two PCB's. My current idea is to use a 0.050" ribbon cable with IDC connectors on ends (although see the end of this post).

When in use, the two PCB's will be laid side to side, and if I then place the connectors in the same position, and I want them to be keyed (say, a shroud with a notch on the side of the odd numbered pins), and connect the ribbon cable, I get something like this is wrong, I'm leaving it here for reference:

i.e., pin 1 goes to pin 23, pin 2 goes to pin 24, ... and so on. The notches on the shrouds are on the side of the odd numbered pins.

My question is: while I can of course figure out the correct pin mapping by simply finishing the picture above, I feel it is a bit error prone (since there's no ERC or DRC checks across the two PCB's in my EDA). Also, I would imagine I'm not the first one to come across this problem, or one of a number of related pin mapping problems (say, stacking boards with connectors on facing sides). So I'd like to find a resource which would give the correct pin mappings for this, and preferably other related problems, but my google-fu has not been strong enough. Is there such a web site?

P.S.: any suggestions on better ways to connect the PCB's are welcome. PCB space is at a premium, I was just able to fit a 0.050" SMD -connector, but on the other hand the connection will be made by the end-user, so it must not be too fragile or difficult to connect. The device is a eurorack modular synth, so the user is familiar with connecting 0.100" IDC for the power, which is why the smaller IDC would at least bring some familiarity to the user. Currents and frequencies are rather small, < 50mA and < 1MHz.