Marcos Maniacs

Hello,

I have been restoring MBG55H for what feels like the whole of my life 
and have now reached the point where I need to purchase a replacement 
battery.
Can anyone advise to where I could purchase the correct battery for a 
1969 2LTR V4?
I live in the UK
Having looked around, local retailers have never heard of a Marcos so 
they don't know the correct model of battery required.
I have taken the measurements of the original Battery tray on MBG55H 
and all modern batteries that I have seen are too large to fit.

Thanks, Mick.