You should investigate the GB Hobby TCU for your Simjet if you are going to use a different ecu. Their web site is http://users.iafrica.com/g/gt/gtrollip/tcu.html
I can highly recommend these units. I did my first series of autostarts on my Moore's Turbine MW54 today with the GB TCU. It uses a Hall-ring magnetic sensor, or IR LED's, as you prefer. The user gets COMPLETE control over the start ramp as well as the idle to full power ramp. EGT and RPM are monitored for full control and safety. They have dealers in the UK, USA, Canada (me), Australia, etc. etc.

Good Luck,
Len