Just to add to the confusion....here's a summary I did from Pierburgs catalogue 18months ago.
Also some notes and links I saved when I was doing the research.
Take it or leave it.

You see the stock is the 7.22355.01.0 - which I could never find a pump curve for....(input appreciated)
the upgrade is to the 7.00228.51.0 used on your higher power (more fuel) cars....I have that curve.

I haven been able to find the 51.0 for less than $355 in Australia and any import would cost me about the same.

PS - the SL55's had an accompanying Pulse Width Modulation (PWM) speed control unit....you don't need that appendage.
How its wired alternatively - GG may help.