I'm using a version 0.4.3 Speeduino board that uses a 40 pin IDC connector. These evidently are mostly used to make it easy to plug a converter cable that goes to an OEM wiring harness (lots of Miata users out there). Here's a pic, the IDC connector is the black rectangle on the left.
Doing it again, I'd probably go with the previous version (v0.3.x) that just uses screw down connections to the board. The differences otherwise are negligible.
There are other options now and coming soon, but probably worth talking to Weaver Markel at WTMTronics if you want more insight.
Back to IDC/Dupont connectors, I bought a big 20 piece pack of female 40 pin IDC shells from eBay via China. I still have 19 of them and would be glad to send you one for free if you need it. If you want to wait for a big pack: https://www.ebay.com/itm/20pcs...a:g:AdkAAOSw7XZXhGru
As I said previously, I hate building crimp connectors so I bought a bunch of precrimped pigtails that I plugged into the IDC connector attached to the Speedy and routed them through a hole drilled in the end of the case that had a rubber grommet. Here's the link to the pigtail jumper wires I used: https://www.amazon.com/gp/aw/d...s_sparkle_scm_asin_0
Like I said earlier, doing it now, I'd probably go with the V0.3.x board with the screw down connections.