Thanks for the diyefi update. I used to look at "diy-efi" until it became megasquirt whereupon the site died. But the last time I looked seriously at DIY EFI was 2005, and that was only because some newly graduated and automotive electronics industry employed self confessed expert made various claims about EMS - ie, what the could not do, or why certain things were done.
But I see DIY EFI very different other than the legal aspect, but that's why I keep to 1960's & early 1970s vehicles - in Australia they are "pre regulation" (aka pre-ADR) wrt to pollution etc. Hence I can take any modern engine, change to carbies or change EMS etc - provided I stay within capacity limits. If it was subject to ADRs (after ~1974), I wouldn't even be able to change the air filter type!
Firstly, like car audio & PCs etc, IMO you would never cut into OEM electrics. You would either use adaptors, or separate looms for more complex stuff like EMS.
Secondly, IMO you would never adapt an EMS/EFI to suit your sensors; you would get the sensors to match the EMS.
If it is a full DIY solution - ie, you are programming and constructing - then of course you can tailor the above to suit, but it might still be easier to change some components.
A classic example of the above is the common use of Delco systems. The typical scenario is to take the entire system from a suitable donor vehicle - ie, Delco sub-harness, sensors, AFM etc, distributor else ignition HEI, may be the injectors. The maps can be changed if required by various means. People can then have the entire EMS system for a few hundred dollars (based on Australian "Pick A Part" wreckers/recycler prices).
Of note, I knew several true achievers that pioneered engine enhancements etc. I watched as they pushed early manufacturers like Haltec, moved thru Autronic(?), "EMS", and whatever others I have forgotten. They all ended up using Delco systems (except for true leading edge stuff).
Since 2005 I've tried to convince others why some features show the limits or primitiveness of some (aftermarket) systems - eg, having 32 selectable maps (gained from dyno testing!). But I live in a country where dual-battery owners have been convinced they need dc-dc converters that can cost over $1,000 to "properly" or fully charge their 2nd or auxiliary batteries. As to the ability to understand EFI & EMS... [ Note - that typifies "public" web forums. Individuals can be very different, as can be private forums and groups. ]
Anyhow, my general suggestion is either Megasquirt, else Delco.
FYI - When I revisited a DIY EMS in 2005, I selected some 32 bit (ARM?) processor. I figured if my 1980's vintage distributorless ignition system (self learning etc) used a 68HC11, an equivalent EFI/EMS deserved an upgrade.