I think the Zetec is probably the best engine swap for the money. I don't have one, so I don't think I could mention anything you haven't already thought of in terms of difficulties (motor mounts, headers, access door in the firewall, etc.). You have your choice between injection or Webers. A buddy of mine is building an S2 with a Zetec. I don't know if he's gotten past all the complications. He's a member of this forum but I don't remember his handle and he's not very active. I'd be glad to hook you two up. He has a very nice set of headers that he had made in England. If you're interested, I would imagine another set would be less expensive for you since he sent them all the measurements. I've attached a couple of pictures.
Good luck. That should be a nice project!