A couple more pics to show current state of build.
Decided not to remove the planks and couldn't find anything suitable at my local model shop to place on top of the existing planking, so opted for stealing a bit of 1x3mm timber from a future part of the project and built up the undersides of the beams. Can't even be seen. (I hope - You eagle eyed ones out there, lose your glasses)
Here is the result.
The first picture shows the one side of the cross section having been sanded and the lower deck floor with the beams in place, dyed and one coat of matt varnish applied.
The second picture shows my first attempt at doing bolts.
I made the bolts by first staining and then applying a coat of matt varnish and then used a sharpie to dot on the bolts.
I tested the process on some scraps of planking.
Tried without stain and varnish and the sharpie bled into the wood.
Tried with only stain, same result.
It took the varnish to solve the problem.
This may not be to the liking of the purists, but the other methods were a little out of my reach with just a desk in the sitting room and my current level of expertise.
Apologies guys.