Hmm. Not familiar with LeMans stuff, but I was under the impression that the underhood light harness was included in the forward lamp harness already regardless if equipped with underhood lamp or not. I could be wrong, but many cars without TR9 in the Cutlass realm I've ran across had the plug taped up in the forward harness. Just run the lamp and its wire and find the plugs and boom, instant underhood light. Too bad yours doesn't already have that.
As far as running the trunk lamp, yes, right down the inside of trunk lid and then along the hinge. On the Cutlass there are plastic wire clips that insert into punched holes on the hinge to hold the wiring in place. Then you can run it any way you want in the cabin, but normally it would be in the wire bundle under the left edge of the carpet up to the fuse block.