This must be a thread I didn't use topic tracker on... Late to reply again sorry.
It''s been a long time since I had to think about which pins are for the OBD connection (back when OBD connection was first introduced the loom didn't carry OBD wires but you got the OBD loom separate with pins already attached to push straight into the connector block). I could check on the pinout but there probably isn't much point - For various reasons good installers generally think it a bad idea to connect the LPG ECU to the vehicle OBD anyway. Never tried it on a P38 but results of doing so on a P38 could turn out to be very much negative unless it's a very late model. Earlier models are not fully OBD2 compatible and although code readers will connect and read live data, the fuel trim info they display might be have long term fuel trims showing at constant -100% or similar. The LPG system would read the same info and interpret it the same way as a generic OBD2 scanner so the LPG system would also read -100% fuel trims, the result of which would see the LPG system subtracting it's maximum range of -20% fuelling from what might otherwise by perfect fuelling.
Onto another question, there are various AEB boards, some look entirely different and contain different sets of components to others. AEB ECU's have been wearing Romano badges for years but King is relatively a newcomer. If the Romano system is an older board it is unlikely that firmware between it and a King ECU would be compatible given the different hardware sets. If the boards are the same year and same spec then if software allowed you to connect to any system it might be more easily possible to change firmware to whichever brand you liked but software doesn't allow that, so although it would be possible it would involve a bit of hacking...and probably not worth the effort when an 8 cylinder AEB ECU these days is about £150... Years ago the same brand ECU only of course of older spec (not truly sequential like modern AEB ECU's and lacking some of the other features too) would have cost over £500!
Other post - Yeah you could make your own single point controller but, like above, would it be worth it (unless you'd be doing it for fun!) when a controller itself is about £50. The AEB175's such as Leonardo's aren't that badly thought out and cover all of rpm detection, stepper motor driving, relay control of solenoids and lambda connection, ability to limit range of stepper motor movement, adjust speed of change of stepper position for rpm, AD converters to read TPS, lambda and much less commonly reducer temp, DA converter for programmable simulation of lambda voltage, serial link to in-cab AEB fuel changeover switch, etc. Not many guts in them but they do a lot for the money and to fully replicate the functionality yourself you'd need to not only make it but program it and maybe write another program for the laptop to adjust it's settings. There are even cheaper controllers (Bingo is one) that have all the basic functionality without the ability to set range of stepper movement or stepper position during over-run, or in fact any sort of connection with a laptop. I've never had problem connecting to an AEB175 using any version of Windows, I have seen some 175's in incorrect branded cases though, e.g. had to connect to a Millenium using Leonado software lol..
Simon