Thanks Shahpor,
Firstly, on closer inspection, the caliper I've bought has the same number on it.
In response to your question, my mechanic has managed to free off the front calipers and we are replacing the pins on those, unfortunately this rear caliper is too far gone after what seems like years of neglect. Wish I'd checked the forum before buying as it seems there is a lot of discussion about this issue with the calipers seizing.