[Buildroot] Installing the 'correct' version of grub

I'm trying to sort out how to get the correct version of grub
installed onto production (x86) system disks.

(I'm currently using the previous release - not the one from last month)

So I need to give someone else the files required to install grub.

Ideally I'd like the 'target' system grub binaries that buildroot
generates to be installed.

But I suspect our procedures are likely to install whichever version
of grub happens to be on the system the disk is actually built on.
While this generates a bootable system, it isn't ideal.

Now I do know what the x86 boot sequence involves.
(I fixed NetBSDs version a few years back.)
But grub2 is entirely too complicated and then hides all the
necessary complication - making it difficult to work out what
is actually happening.

What I'd like to do is populate the /boot filesystem with the
required files (which seems to be a lot!) and then run the
command to initialise the mbr and pbr sectors
(actually sector 0 and the first 8k of the partition.)
But grub-install seems to want to copy everything into /boot.

Now I've set BR2_TARGET_GRUB2_INSTALL_TOOLS to get all the
grub2 'bits' into my root filesystem (an easy way to get then
into the image I give production).
If I mount that filesystem and pass '-d /mnt/root/lib/grub/i396-pc'
I get an unbootable disk (resets instead of showing grub menu).

I also can't actually run grub-install when I boot the disk.
It wants some files that are (IIRC) usually in /use/share.
(There is no requirement for this to work.)

There is also the practical problem of the version of grub-install
to use.
The 'host' version that buildroot generates is likely to on
whatever system 'production' use - so I can arrange for that
to be used rather than the host's own copy.

Does anyone know if grub-install ends up writing a sector
list into the pbr?
The NetBSD versions all managed to read the filesystem in order
to load /boot (even the FAT one which has to fit in a single
sector rather than the 8k that most filesystems reserve for the
boot code).

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