[Dragncar]

If you have a 428 that runs good, nice lump to the cam you might just want to leave it as is. Just getting a new hft cam to seat correctly to a new set of lifters can be a real challenge. You can do everything right and still end up with a flat cam.
The Tri Power does have a certain cool factor, but its not correct for the car anyway. Might not run any better the the Torker and Edelbrock(I don't like them) carb.
Myself, I would put a nice Holley 750 DP style carb and a RPM. Or.............. that new Victor Jr intake.
A new electronic distributor won't get you anything over a correctly done single point. But those new ones you can tune with your phone/laptop have some value on a street car.
Congratulations on your new venture into the Pontiac world. You are now one of the cool kids. And a 68 GTO with a 428 and 5 speed on the street is defiantly cool.