does anyone know how to identify the version of ECU that a car is running?

Also, does anyone know if the ECUs are interchangeable as far as connections are concerned (I understand that some remapping and other items like TPSs are required too) if you are upgrading from a L1 to a L8?

 

l1 to l8 is easy you need an l8 which has a white fuel screw and no wings on the side of it unlike thl1 and you need a 4x4 tps and the tps plug is inverted because the wires are oposite way around

 

ECU types used in Sierra (RS) Cosworth:

All type of Sierra (RS) Cosworth use a Weber Marelli type of ECU (Engine Control Unit or motormanagement) however, these ECU's have changed over the years as demands grew and computer technology improved.
Although, as far as known, all ECU's use the same connector pin-out (und thus can be electrically interchanged) one can not use for instance the latest ECU on the earliest Cosworth. This is because the ECU is fully "tuned" to the engine characteristics which have dramatically changed over the years. The latest ECU's also use input from several additional sensors which are not available in older models.
Here is an overview of ECU's used and how to recognise them:

Level 1:

Used on the RWD hatchback RS Cosworth, has 64Kb of memory. Can be recognised by the mounting flange on the front face and a yellow CO adjustment screw.

Level 6:

Used on the RWD sedan (RS) Cosworth, has the same capabilities as the level 1 model but uses totally different electronics. That's why Level 1 and Level 6 chips can not be interchanged.
Can be recognised by the mounting flange on the front face (like the Level 1) and a white CO adjustment screw (Level 1 has a yellow one).

Level 8:

Used on the 4x4 sedan (RS) Cosworth, has twice the memory storage capacity (128Kb instead of 64Kb) as Level 1 and Level 6. That's why chips can not be interchanged.
Level 8 was available in 2 type since the engine in the 4x4 was available with and without hego-sensor (i.e. with and without catalytic convertor).
Can be recognised by not having mounting flanges and a green or red label with WD48.08.
The one with the green label and second code IAW048/01 is for the catalytic convertor (US83) model.
The one with the red label and second code IAW048/02 is for the non catalytic convertor (15/04) model.
It is uncertain if units/chips can be interchanged between red and green types/engines.

There are also Weber Marelli P8 (no flanges, white label IAW48/P8) and Ford EECIV (totally different from Weber Marelli, central bolt to hold connector) ECU's around. These are however only intended for use on a Escort RS Cosworth but you might find them in some motorsport Sierra's (RS) Cosworth.