What part number was the unbranded one supposed to match? 24436738 to fit an Omega B?
Or was it sold as fitting an Omega A, Senator B, Vectra A & Calibra?
Yes, I bought that to my Omega B. I could put them one upon another and take the new pic. I think they are similar (L&R).
So you bought the unbranded backplate as fitting an Omega B, which is fine.
However member addy asked about using Senator backplates on his Omega B? So what's still not answered is whether or not Omega A/Senator B/Vectra A/Calibra backplates can be used on an Omega B? EPC suggests not as they have differnent part numbers.
The old style Omega B pivot pins, with the crosshead, fit into the backplate from the outboard side. The new pins with no crosshead fit through the backplate from the inboard side. Either pin can be used. No need to change or upgrade the backplate. unless damaged. However to fit the newer style pins, without the crosshead, you need to loosen the four bolts and temporarily move the plate outwards so the pins can be installed. That's the GM service instruction.
The same service instruction is true of the Omega A/Senator B/Vectra A/Calibra pivot pins. The new style pins can be used by inserting them from the back of the plate.
Member addy shouldn't need to change his plates unless the locking slot is too damaged or corroded. There is no need to upgrade the pins for the new type if the plates are in good condition. Is's just that the new pin type, inserted from the back, are less likely to pull through the plate as they have a bigger contact area.
I definitely didn't loosen the 4 triple square bolts when I put the pins in from behind - I didn't have the tool to undo them. Quite how I managed it I can't remember, I think I spent a long time trying to feed the pin in from underneath the trailing arm before trying from above and then it just slipped in
On the subject of service instructions...... I have lost count of the times I have followed Haynes and spent days doing a 5 minute job, hopefully the GM service instructions are more accurate