I am helping my 15 year old grandson with his first car. I have read somewhere there are later model mustang seats with headrests that will easily mount in the '68 with similar styling. Does anyone have a hint at what that year might have been?

 

I would think that '69+ high back style buckets should go right in, not sure what is involved though - guessing that the brackets probably need to be swapped. Try posting this up in the Classics section here, shouldn't take long to get the specific answers and direction you're looking for.