I was sent an old photograph from a friend of when I and he were in the RAF Cadets (CCF) back in 1968/69.
We were trying to lock down which RAF Base it was.
My friend suggested RAF Coltishall which we certainly visited, and even stayed for a weeks camp.
I however checked out the aircraft number which was only clear from the very top i.e. you could not see the intersection of the X but enough to know it was an X, similarly the next letter was probably a V or could have been an M, none of the numbers were visible other than all three had curved lines at their tops such as 2,3,8 or 9.
The Squadron markings were clear and were 111 Squadron.
While researching I came across your site, I am sure that the aircraft must be the Type 5 you refer to but the markings are definitely 111 Squadron which I believe was also at the same base.