There is not a lot of space in the boot of the MGB so you need to maximise all the space available including that in the centre of the spare wheel.
I found a piece of drain pipe the correct diameter to act as a spacer to clamp the the wheel up side down. It’s surprising how much you can get in that space. I bought a wheel cover to go over the wheel and all the bits in it.
Looks a neat job when done.