How can I get more power from a 428CJ?

[ERA Chas]

Nothing suggested here will give the meaningful improvement in power you seek except a cam change accompanied by head improvement or change and carburetor improvement, as Brent suggested. The other ideas are fine to augment those basic changes.
Those changes will alter the docile performance you now enjoy so be certain what your desires are.
Start by going for rides in cars with several levels more power than you currently have. Then decide what you want to live with. I have in mind a certain blue/white car with magnesium wheels as the upper end of the scale for power in proximity to you.
The actual parts and procedures are easy to ID and source from the forum then.

[PurpleVenom]

My path to 50 rwhp gain and 40rwtq as follows:
- Changed to higher flow air cleaner/filter - K&N - yes, this was 10 hp and 10rwtq per the dyno
- Port matched my intake to my heads (460 - Torker 2 intake - Cobra Jet heads) - this was 40hp and 40rwtq per the dyno

I realize my engine is a little different and the intake/heads aren't quite the same, but check this first. The above cost me $250 + dyno time. Timing set to 18 initial and 38 total (mechanical advance)

Good luck!

Tim