What you are saying is that the SparkFun part uses the transistor to invert the logic? When the opto is "on" then the transistor drains to ground which turns the MOSFET off, right? That means that when the opto is off the MOSFET is on. If this is true, I need the opto to be on whenever the microcontroller ISN'T sending a signal.
Anyway, about gate drivers, if I used one, would I just connect it to the OUT from a NPN transistor, with the base connected to the collector of the opto and to +HV, like the SparkFun circuit? Then could I use this (
https://www.electro-tech-online.com/attachments/gate-driver-jpg.31391/) without the resistors? Actually, I'd still have the farthest right resistor, 100 ohms, but it would be in front of the entire circuit, on the PWM in line.
By the way, would it be good to have a Zener across the gate to ground? You said the car battery can spike to 80V, which could destroy the MOSFET. I could use a Zener to clamp it at 20V.
I don't have an alternator on this. Remember, not a real car. Still, the cap can reduce noise from the engine.
For sensors, I have a Hall Effect sensor on the crank flywheel, a MAP sensor, an IAT sensor, and a "throttle position sensor" (it isn't really sensing a throttle position because it controls the throttle position). I am using an electrical valve train, which is what the solenoids are for. This means that I don't need a cam position sensor.