Which PT&G bottom metal? Very easily done with a sharp chisel and gouge if the bottom metal is BDL style. You can enlarge the guard screw holes for pillars with a hand drill if you're careful and have a bit of skill using hand tools.
The lay-out for the job is the important part. A set of snug fitting guide pins, one for the front screw hole and one for the rear, will help keep things lined-up. Need to be long pins, so the new trigger guard assembly can be slid on them. The advantages of having machine tools to make what you want when you want it! Additional; a couple of long 1/4" x 28 bolts with the heads cut off will do in a pinch. A 'snug fit' between pin and hole (in the stock) would be best, but not always available.
I've seen your tracks in my stock building thread. Think about making a template for the bottom metal and the simple jig to clamp your stock into. Look at page three. Just make the template tight to the bottom metal. Cutting the template allows you to use a router with a bearing bit. It only takes about an hour to make the template.