Sorry, but I don't think I'm following.
The camera shot HD but you edited in SD. Why did you have to do this? Did you edit this in FCP?
You now want to start an HD FCP project and bring the SD edited video into the new project?
Could you give some details of what you're trying to achieve?
Yes. A couple of ways that might work.
What you need to do is load one of your hd clips in the viewer and edit into a new HD sequence. Does it display correctionly?
OK, select the clip in the hd timeline and copy (command-c). Now go to the HD sequence with the material that's distorted. Select all (command-a) and paste attributes (option-v) and choose basic motion and distort. That should maek things work. What won't work is anything that you've adjusted as far as basic motion or distort in your PAL sequence. That I'm pretty sure you'll have to redo.
Choose your original PAL sequence and do a Media Manage changing the sequence preset to the appropriate HD paramenters with the media offline. You then should be able to reconnect these clips with your original HD media.