There are a lot of EFI systems out there. Megasquirt (MS) is one of the cheapest, and is close to be being the most configurable.
Ok. Now three options on how to do it.
1. Modify an old mechanical fuel injection system to take modern EFI injectors and add all the sensors.
2. Get a close K or Djet and modify it. Close to the easiest to do.
3. Get a single carb manifold, and adapt a TBI to it and use MS. The TBI has most of the sensors built in. You can get a Pontiac/Chevy/GM TBI from the iron duke 4 cylinder and it almost everything in one unit. If you do a search on the threads here, I am in the midst of doing this with my 1966 200.
The greatest advantage (other than price) to the MS system is it's flexibility. The biggest downside to the MS is the flexibility. Makes it harder for people not familiar with EFI to get it working. Take for example the SDS efi. They sell you the ECM with harness, injectors and sensors as a complete kit. It also comes with a tune close enough to use. And adjusting it is fairly simple. But, it cannot control a TBI like a MS can.
The Porsche 914-6 in my signature is Megasquirt. It use the old CIS system that has been modified to accept modern EFI injectors. I then mounted all the sensors, and tune the MS to work. Works well. If you do a search on youtube, you can find a video of it running with some install details.
Well, there is a lot more, but this would be a good place to stop.
Hope that helps.