Has anybody tried this build on a H5 or do they know if it will work on that please?
Give it a go? Although its a different box, I strongly suspect it has a chance of working simply because the H5 was nothing more than a marketing re-release so zgemma could tout 4K. It's essentially a H2H with a slightly different processor.
It's not 100% exactly the same processor - but it's 99% there. I'd strongly suspect the logic board is identical as the processor is an exact drop in for the one in the H2H - the only thing that may differ is the tuner.
If it doesn't work, your bootloader should still be intact so you won't have bricked the box and can just reflash a new image.