[gthompson97]

MSD ignition will give you a stronger spark, but it won't have any effect until you're pushing some major horsepower. Pointless mod IMO.

Bette fuel injectors are also pointless until you need them, they will do nothing for you.

The link that clipsekid listed is about the best upgrade path you'll find. The 420a isn't a very good "power adder" engine without the turbo. You've done about all the bolt on mods that you can. You could try get a safc-II and maybe tune it a little, but I'm guessing that you don't know much about engines so that would be a good mod for you.