Don't have any clue how to change to EDIS with the current system, but if I some day do that, I will definitely be using MegaSquirt or similar. This EEC-IV even gets the info of RPM from the distributor's hall-sensor. For now the EEC-IV will do it's job, even for possible turboing I think I'm gonna just use some extra-injectors and if needed do one little trick to adjust the ignition timing a bit later.
Only head I have is the one I have on the car now, but it will have to go before I can put some boost to it. It's ported & lowered with nice cam and stiff valve springs, so I should get some nice money out of it, in mint condition too, no any wear or whatsoever.
But, I actually remember seeing some iS heads on sale with price of under 50euros over here, good ones I mean. A bad one in need of some work would be possible to get for 20euros I think.