I don't really see an easy way to accomplish what you want to do, I'd probably just shoot the rifle as is and be happy.
I was reading all the things you said would be necessary and thinking the same thing. It's a $150 rifle to begin with. Does it make any sense to put a lot of money into it? You can buy some quite inexpensive modern rifles that will outshoot it any day. Or if you really do want to go full out custom, I can think of better places to start.
I have an M48 myself. I've just left it totally stock.