KE3 doesn't really need any piggy back fuel control. Literally 2 of them identical to any 103 setup is bolted in a twin setup on a Ferrari Testarossa. Stock out of the box they are rated for as much as 70% fuel requirement increase without any modification. The Lambda loop its fuel control module operates has 5-6 bar of fuel pressure to work with and has no problem at all maintaining stoichometric with vastly increased fuel delivery requirements without any modifications at all. Note also that WOT switch on the linkage disables the lambda loop for full throttle enrichment so that's not an issue either.

The KE3 problem is spark mapping, since it doesn't have a knock sensor it is like an early electronic ignition setup, little better than a points ignition system in that it is designed to pre-emptively prevent engine knock rather than dynamically prevent it like modern EFI. So you never get quite as good a spark advance as you could, due to the error margin required with predictive systems and it retards when it may not need to, finally an end user lockout means you can't remap it for custom camshaft profiles or forced induction conversions so you never really get the most out of a dramatically modified engine without a spark ECU piggy back you can map.

That is, unless like me you got super lucky and happened upon a genuine AMG 3.2 ignition module in Amsterdam and installed that to recurve your spark for a hotter camshaft. Still not as good as EFI but much cheaper even at the collector's price of an original M103 AMG part.