after some advice on wheels to fit avon have found rear hub center is bigger than the front and will need to keep speedo write will some old ford wheels fit? is 6.5x15 et39 write?

I've got 15" x 6.5" with ET38 offset. Fit fine. 7" width should also be okay too. Smaller than 15" diameter and you can have issues clearing the large rear uprights, unless you modify them.

Normally Ford fitment of PCD 108 is used. My wheels are multi-fit: 108 and 100, i.e. 8 holes.

I used to run 14" wheels ET24 with no issues. I've since changed to 13" ET35, but I had to modify the upper rear wishbone.