Get him the appropriate hardware and software for the PCM in his car. I will soon be getting a Quarterhorse for my 93 Lincoln Mark VIII:
With one of the software editors, Binary Editor:
And or perhaps EEC Editor:
You need an unlocked strategy and bin file for your car and with that in place you can control and tune your car to the moon. Dtat logging in real time for real events is a very powerful tuning tool.
My EEC-IV is actually an Intel 8061 and you can get even further into that with a disassembler etc.
Lots of fun tuning with modern cars. I will have switchable tunes when I'm done. One for mileage and one for power, for starters.