Re the joints in the stock rail. I suspect (purely based on observation) that
switches were produced as a pair of planed blades and stock
rails which, together with crossings, are assembled on site
using plain rail to join them up. Hence the joints near the
hinge - and also just beyond the blades. I too have seen
photos with the joints opposite the hinge which as you say this
was probably to aid transport and lifting - especially appropriate
for the WW1 field railways. However, I suspect this is a much
weaker arrangement. In model form I think all these joints should
be cosmetic, i.e. use continuous rail with fishplates added and a
notch in the rail head if you are really pernickity like me.
As to Sn3 I used it very successfully for the hidden track (all
15m of it) of the PLR at it's recent outing. I believe others have
also used points - perhaps with some filing of the check rails.
Finally I'm sure many would welcome a to scale plan. If you are
willing we could host it on the main group website with supporting
info as per your original post - send me the info direct if you
are OK with this.