Finally build the IR PCB and it works fine.

One issue: I forgot a pin header and had to make an ugly workaround:

Other (small) problem: the green leds are very weak (look the led bar at top, it is showing the 01010101 pattern). I measured the 74ALS874 output and it reads only 3,5V, and while it is still inside the TTL standard, I am used with 5V on outputs. So I will need to lower the resistors but it is a simple and painless change.

TTL accepted voltage levels:

Thanks for reading.