Happily, scans of the old 15 minute topo maps are available. The easy thing is to simply use these -- then this project is just a minor step from the Mt. Fagan project.
For the Mt. Fagan project, cropping the maps was optional. Here it is important, otherwise things will be a mess where the two maps meet each other.
It will be worth investigating whether two raster layers can be merged into one. Otherwise we will have 4 layers (along with a "scratch" points layer.
This could spawn a second project. The eight 7.5 minute quads that made up the two 15 minute quads are available. These could be used as a nicer topo base layer in lieu of the 15 minute quads. Here cropping will be even more essential.
Tom's Geology Info / tom@mmto.org