Hi Colin
See link re expansion tank same as MGB 1976/81, however the bracket is modified by Morgan to fit the 4/4. You can used the bracket shown on link with a 90degree upturn bracket which would have to be fabricated. Could look for a tank and clamp on Friday at NEC and send up to you, if you like.

http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=151

Kind regards
Phil C

Phil C
Morgan Plus 8 4.0
Morgan 4/4 4seater 1.8
Volvo XC70 D5 220
Mazda MX5 2.0 Sport