I have fitted MS to both my Landrover, and also my P6.
The Defender is fuel injected, whilst at the moment the Megasquirt on the P6 is only controlling ignition. The installation (so far) in the P6 is covered in my project thread, and starts around here with the fitting of the toothed wheel etc. Note that I was controlling the ignition with a Megajolt unit at first, which is different to Megasquirt as it only does ignition and cannot do fuel. The Megasquirt was fitted a few posts later. In both instances the MJ/MS were controlling a Ford EDIS module, running Ford coil packs:
http://www.classicroverforum.net/viewtopic.php?f=21&t=16625&start=105
I built the ignition map based on the Rover figures published for my model of distributor.
EDIS 8 modules can be bought from suppliers here in the UK (no Ford V8's here, so none in the scrappies) or you can do what I did and buy from the US on ebay - EDIS modules are about £40, and coil packs can be had for a fiver each with leads if you are patient. The coilpacks are plentiful and were fitted to all late 90's/early 00's Fords.
That all said, if you go straight in with Megasquirt you can control many different types of ignition, including COP or Coil near plug setups; you are not limited to using EDIS only. Another option is to keep the dizzy with the advance mech locked out and MS controlling advance through that - this does give you flexibility of programmable advance, with the period look, but you will still have some inaccuracies in timing due to slop in the dizzy - this is completely eliminated with a crank triggered setup.
In terms of how easy it is, then the steps you have to go through (for EDIS ignition and fuel on an already EFI'd engine are):
Buy MS kit (or ready made) - see
http://www.diyautotune.com - The MS2 v3 kit I have in the P6 is here:
http://www.diyautotune.com/catalog/...le-efi-system-pcb30-kit-black-case-p-119.html
Fit trigger wheel and VR sensor
http://www.trigger-wheels.com
Mount EDIS module, coilpacks, Megasquirt module (MS should not be mounted in the engine bay).
Wire everything up (see manuals on
http://www.msextra.com)
Fit Manifold Air Pressure line to manifold and pipe back to the MS (you can bin the AFM on the hotwire).
Fit a wideband oxygen sensor - you will need one to tune fuel. Spartan widebands have a good rep from
http://www.14point7.com
Then the real fun starts, setting it all up...
You must check that your timing is correct with a light. When the MS is commanding a figure, that is what you should see with the light. This is crucial in not blowing stuff up. If you find that the timing is out by a couple of degrees, that is ok - you can adjust the "trim" in the software to compensate. If it is wildly out you will need to adjust the wheel/sensor position until it is close.
You need to calibrate you throttle position sensor (TPS), Inlet air temp sensor (IAT) and Coolant temp sensor (CLT) - this is all covered in the Megasquirt manuals.
The MS has a "base map" that should start and run your car, this is not optimised in any way. You will need to input your ignition map, and target fuel map. You can then go out for a drive with the laptop plugged in running "Tunerstudio". This has a whizzy feature called "VEAL" which will update the fuel table as you drive until it matches your AFR targets.
Once you have your ignition and fuel maps you have to tune the other bits like Acceleration (AE) and Warm-up enrichments (WUE) - Tunerstudio also does automatic WUE tuning, which is nice.
Tunerstudio is free, but you wont get VEAL in an unregistered version - I think it is about $40 to register, which is well worth it.
http://www.tunerstudio.com/
Once you have the fuelling and timing all done including cold starts and accel enrichment you can move onto whizzy things like closed loop idle control (if you have an Idle air valve fitted), controlling your electric fans, shift lights, launch control/flat shift etc.
I would say that if you want to fit EFI and forget, then stick to the Hotwire. If you like a project then go for MS - its an interesting learning experience!
