MG? Must have been the Clenet. They were however based on late 70s LTD IIs or Mercury versions. Some used Town Car or Continental grilles. Smaller versions used MG doors, glass, and trunk lids. The larger ones used VW Super Beetle glass and doors, but all had Ford underpinnings. I remember applying for a job there in Goleta and seeing the half disassembled Fords in the back of the shop. They would sell those to body shops.
Of all the 68/69 GM mid size cars, the Buick looked very nice in my eye. The side sweep detail was great. Didn't hurt that my Grandfather had a new one and I later owned a 69 Special DeLuxe. The Chevelles were chunky and Olds were bloated. The Ponchos were pretty cool though.
Futurattraction (Forum Member) has made Futura two doors in a stock and pro street configuration. That would be your beginning piece. They are resin bodies but would give you the beginnings for converting to a wagon. Fox platform based so a Mustang kit would donate the running gear/drive line.
OK, I went to open office and was able to figure it out and made several images of what i wanted. A 1955 Ford dashboard which also got me the proper emblem. Figured the sizing thing and hopefully I have what I need. .