Genuine Acorn VFS ROM, identified by the green sticker, is now in, as is the replacement battery pack.
This battery pack is in fact rather ingenious - the usual holders for 3 AA batteries won't fit down the side of the keyboard, and the other space - between the PSU and the main board - is taken up by the AIV SCSI board. Instead, an AAA holder is used, which is just the right size to pop next to the keyboard!
I don't claim any credit for this, I would never have thought of it; I received it in the post from a very kind gent. who could see the problem I was having!