Well that's an awesome photo! Presumably you had to remove the rails/threaded inserts? But sure, everything should fit in 3U. There's been promise of ears for 19" rack mounting for a while but those are still on the way.
Not long until the modules are ready. But summer holidays can result in a slowdown sometimes.
Btw. with everything in the case like this, probably you wouldn't need to use the line drivers at all. Just connect J8/9 and J19 to the respective digital and analogue expanders.
Here are some order numbers for IDC sockets from Reichelt:
10 pin: „PFL 10“ €0,11
16 pin: „PFL 16“ €0,19
24 pin: „3M 36266600“ €2,25 (only available from 3M, actually I like the cheaper PFL more)
Shipping cost to France: €5,60