i'm very happy with it, thanks everyone for your help. worth noting that I saw a mk VI alto neck (lacquered) for over £800 (ye gods) and was offered one for £500. this mk VI alto was an army sax and thus has no engraving (and is incredibly shiny due to years of parade-ground polishing). it is now I think saleable, and true to form I no longer want to sell it since I keep taking it out and tootling on it.
that's a point. Stephen, but on the other hand I didn't buy that one! I saw one for over £800 on e-bay, but I think they will wait a while before they sell it. the silver neck I also bought was about the same price as yours - they are over £1,000 new. I think it's all a question of waiting, I have had this sax for 7 or 8 years with the sba neck on it, and it always played fine like that. yes, and it works beautifully with the neck you provided.... oh, I must do something about that blu-tac.