Did you resolve the problem? I've got same issue, code was for trans speed sensor. You can manually shift 1st to 3rd but no overdrive 4th. Careful with the shift down because it doesn't slip through the gears.
If the immobilizer is active while cracking, you will see the SVS light flickering (car & wrench symbol). If check engine (or SVS) light is on, it could be a cam or crank sensor.
Are the fans operating (cold start) when you turn the ignition on?
Awesome specimen! I had one exactly the same spec! I thought it was the only one. None really left nowadays. I hope you've kept it, it's a really special car!