Sorry, i wonder if i am not quite understanding you, but in a nutshell...

Escort Rs Turbo CVH... no problem..

EFI from Fiesta OFAB = No problem.

Chip to suit the 2.5bar map sensor.... PROBLEM.

Driving with that sensor on a system mapped for the stanbdard 2 Bar = PROBLEM.

Solution = get chip for the 2bar, or get it live mapped by a specialist on your 2.5bar or 3 bar.

Why cant you use a 2bar as std?