Starling, thanks for your reply.
I did now obtain a PCB of same P/N but from 40Gb. Drive still seen as "Mammoth", 40GB and s/n "WDC-ROM XYZ--". So I transplanted ROM from original.
But I think ROM has been cooked too, as the donor board now does nothing, no spin up. I did notice underneath the rom there were four marks next to four of the pins on one side, so I'm guessing it's cooked
But I do notice that the PCB from the same model is used, I can enter Marvel utility and read all SA modules OK. But drive is seen as"Mammoth" and serial number is seen as "WDC-ROM XYZ--" or something similar.
Suggestions?