Success!
After discovering that the steering protector had to come off....that meant that the fairlead plate had to come off...then that the motor mounts had to be released and the engine raised a bit, the old box came out the bottom with the appropriate vocabulary.
I'll be dipped if the replacement (new) box would fit back up that way though!
After removal of the PS reservoir, the new box fitted down from the top.
Yes, I'm pretty sure that the removal / replacement would have been easier if the PS pump hadn't been in the way.
No, I don't know who fitted it...it came to me that way.
Thanks!