The chassis would have been wider on the plus 8 in those days, having said that its only the length of the horizontal angle iron that varies as far as I can recollect. I have a towbar on my ‘69 4/4, Factory supplied.
1969 4/4 1995 plus 8 1996 Plus 4 4seater 2002 Aero S1 2013 M3W 2014 Plus 8