M&W pistons and LP manifold (I think that's the only gas manifold you can get new) brought my G up to 55hp. I was very happy. Switching from a mag to a distributor won't gain you any power, but you can convert the distributor over to electronic ignition. The old points work fine, but the electronic ignition is maintance free. I did it 5 years ago and haven't had to touch the distributor since. I've since put in a reground camshaft, that got me to 58hp.
That's a nice looking G! Wish mine looked that nice.