Since, no one is chiming in, I'll give my you two cents. Boot boards were often thrown away because they were a Pain. Many mini owners were not patient in taking them out or putting them back into the boot, especially if you had battery problems. The boards had to lifted on one side and turn. They did not go in or out smoothly. You don't have the twin tank, which means you can have a bigger board. This bigger board just adds to the problem.

If I were you, and no one chimes in with dimensions, I would make a template from a large flat of cardboard or foam core. I do have the twin tank board.

Yes for a single gas tank, a MK1 Austin Mini

Are you referring to the boot board?

Does anyone have a template or dimensions for a boot (trunk) self for a MK1 Mini.