DETP

GTSBoy makes a sound argument, however having been is similar situations myself where I couldn't afford or justify purchasing a aftermarket ecu, there is always a way. Projects like this provide an opportunity to learn alot. Here in NZ we have trademe and over the years I have bought a few older standalone ecus for around $100. Your proposed setup would be far from perfect, but it could work. Detonation is your enemy here!, run good fuel and build a listening device.

If Disaster occurs, it will be due to detonation. Start with setting the timing a good few degrees retarded and you will need to listen for detonation, you can build a little knock listening device cheaply and easily, a wideband would be very useful to monitor the afr as well.