I would get a 2nd engine priced up with fitting and workout which is cheaper in the long run, you said it would take a week if you have the rebuild so gives you a bit of time . But as Jay said depends on how much you like the car I guess. £1200 seem's about the right price for te head to be done as said in the other post.
And not tell them
I wont tell you what or what not to do. I wouldn't myself but I'm the sort that gives the car an oil change new breaks and pads before I sell it :D