Craig,
The 5" gauge is the distance between the rails.
As the prototype is 1 m gauge ( 39.37 inches ) a scale of 1:8 will be used.

I already have a similar unit running, 2 x 300 W 24 V motors off 48 V from 3 x 12 V car batteries, two batteries in the loco and one in the 'bum-truck'.
It can haul 6 adults on level track.

I have applied the projections to the photo and get the Horizon Line running through the headlights.
The camera axis I used was simply in the middle of the image.
I will examine the two posted images closely to see if the axis position can be improved.

The written description of the projections is still a work in progress.

John