Clifford? They've proven to be erratic with supply times. Some people have got stuff almost the next day, others have waited months.
To further complicate this issue, inquiries about unfilled orders have at times been met with responses that haven't instilled confidence...
I am not sure if any of the headers AzCoupe sells would fit. The last bit of pipe which is more parallel to the floor, may end up too high on a 250 - either striking the firewall or floorpan braces. He will advise you as best he can, if you contact him.
250s may become more prevalent in older Fords over the next couple of years, so it could be that something rare now, is more common in the future.
Regards, Adam.