Mike,
You haven't said what you'll use the hammer gun for. Nor do I know how much hammer gunning you have done. I'd advise starting with function: if you are going to hunt with it, can you cock both hammers in one sweep of your triggerhand thumb when the birds flush? That's really the only sensible way to hunt safely with other people (sorry, walking along with a shotgun open and the hammers cocked is never going to be right for me).
Purdey is a brilliant maker and sleeving etc. should be no problem at that price. If it fits, buy it -- if it can function nimbly and safely in the field.
Regards, Tim
