(Plugs in, cut and sanded. Pics below).
Rail bolt holes countersunk, shims shaped.
I had intended to finish it today but the sealant that I bought is permanent, rather than semi-permanent, so I shall aim to finish next week.
I also cut some plugs to cover the bolt heads. The ends of the rails need rounding off, and the edges too

Plug cut down with saw. I used a steel rule to protect the top of the rail from the saw teeth, putting the ruler between saw and rail.

Just need to round the ends off and then oil. Or Cetol, which gets lots of positive support. It has a slightly amber hue, but will be good for two years, if looked after. And I have a new tin. So I think it will be Sikkens Cetol.