Bob's right - the metal plates are thinner than the wooden ones, so installed in the existing routes, the plate will protrude from the back of the instrument.
If the electronics and the remaining wood allow, you can make the plate shelf deeper to accommodate the thicker plate.
The original continuous wood backplates were a veneer applied to a brass plate. This didn't work out well with Coco Bolo and other Rosewoods (cracks!), but did okay most of the time on other woods.
You can swap out plastic for wood as far as thickness is concerned. In any case, we need the original plates back here if we're making them to assure a good fit.