Hi Arthur,
Unfortunately I cannot remember the lengths of the bolts. If you don't have a convenient supplier of bolts, maybe you could use threaded rod as Phillip suggested. A 1m length will be more than enough, 0.5m would probably do. There are only three bolts in mine, and a mate's Mark 3 also has only three bolts, so this may be the standard arrangement.
Washers are not required.
I don't know what the life expectancy of Nyloc nuts is underwater so I would be inclined to use a marine sealant, or Locktite if it claims a long life underwater, or locking nuts as Phillip suggested.
I found that some of the polyester putty came away with the shoe, and some remained attached to the fibreglass. I removed it all from the shoe and all the loose stuff from the fibreglass, which left large cavities between the shoe and fibreglass. I used epoxy mixed with filler between the shoe and fibreglass. I was concerned that I would not be able to remove the shoe in future if the epoxy stuck to the shoe too well. To prevent this I wrapped the shoe in clingfilm and wrapped PTFE tape around the bolts. I removed the tape at the ends of the bolts and used Sikaflex around the ends and nuts. Hopefully that will stop the nuts coming off. I don't really know whether I did things right.
There was a thread in 2017 discussing the shoe and bearings which you may find interesting.
viewtopic.php?f=6&t=1980