[ERA Chas]

If you're just looking for 'make work' to keep your hands busy and wallet empty-just leave it and drive it. The normal maintenance and trouble-shooting will be enough to keep you busy.
If you're a real go-fast guy and drag race or open track it (the 428 not good for that) there's lots to do. But a more aggressive cam alone (you'd need better springs and check p-to-v clearances) might get you 20HP if you pick smart. You'd need a coordinated plan of heads, cam, exhaust and intake-$$$ and a constant chase to get all running right.
You've got a 450HP combination now (if it's set up right) and would need another 100HP to ring your bell enough.
If your speed experience is good enough (power to weight ratios in the 5's), clutch is good, just buy another bullet-like a 600HP/482 from one of the quality builders on here and just swap it in. Sell your 428 on the FE forum. Then hang on.