Metering Head Part Numbers

I have two metering heads for my EG code 1.6 engine, the first came fitted to the car and is:

Bosch 0 438 120 189
VW 049 133 353 AA
When I search those part numbers the most helpful information I find is the same units listed on Ebay as for a Mk1 1.8.

The second I bought from an EG car being broken, and its part numbers are:
Bosch 0 438 120 035
VW 049 133 353J
When I search those I seem to find Mk2 1.8 units.

Now I know these are the part numbers off the air flow meter section, and that the fuel distributor section has a seperate part number, but I'm assuming they have been swapped as a pair like they usually do.

Looking on VAGCAT I have found the part number 049 133 471 D which is for a 1980 EG GTi

So unless the above is wrong, I have the incorrect metering heads, my car has run from the AA head for the past 10 years without issues, although I assume it would over fuel.
Was intending to rebuild one of the metering heads to chase a stutter but would rather start with a unit for a 1.6. What is the technical internal difference between the 1.6 and 1.8 metering heads?

 

Ptrobaly no difference contact Martin Challice (grey Goose Restorations)