[Coley]

In my opinion...this all boils down to you and your budget.
You will get every opinion from 'live with it' to 'spend $10,000' on it here.
So....do you have a budget on this?...if so, what is the maximum amount you are prepared to spend to resolve the current problem?
Is your truck an all original 'high dollar' vehicle?
Are you ok, if the engine is not original?

Here is what I would consider...noting that I am not you and its just my quick take on this....
I would pull the original engine, prep it and store it and keep it available for a leisurely, budgeted rebuild some later day. (if you decide to sell the truck you will have the original 396 available as high quality 'bait' for the new buyer)

Then...if I had a tight budget...I would watch for a quality, used 454 and detail that up as the original 396, no one would have to know and they basically look identical and 'drop right in'....and you would probably really enjoy the power/torque difference.
You can pick up a good, used (compression tested) 454 for a lot less money than a rebuild or replacement on your own....just make sure you know its condition when you buy it.
Note: I've seen a lot of low mileage big blocks pulled from wrecked motor homes lately and the guys usually aren't asking an arm and a leg for them...and a lot of them have the TH400's still attached. Now these aren't 'high performance 450hp '454's but they are still big torque big blocks that will easily get a pick up rolling out quickly....and I would thoroughly check any candidate out with a compression test, etc.

That used engine, although obviously not new....would easily give you a few more years worth of fun, driving and entertainment...and in the meantime you could form a plan regarding your original 396 and what you want to do with it.

(note: I just did a quick search on Seattle's craigslist...its full of them for reference sake)

My two bits.

All Good
Coley