Man, 6,000 miles divided by 30 years equals about 200 miles per year...
Anyway, it sounds like you just want it to run as good as it looks, and right now it doesn't quite cut it. As was already said, 100,000 miles is quite a bit for a car of that vintage. Does it show any of the usual signs of being worn out, like blowing white smoke out the tail pipe??? If so, I'd rebuild it to stock specs, AND do what's spelled out below. If it doesn't show signs of being worn out, you might just want to spend some time fine tuning it like checking the rotor phasing, maybe degree the cam, and figure out if re-jetting the carb might pep it up a little. Just my thoughts...

Why not to stroke the stock engine from 383 to 426 ? it won't harm the block, original crank can be storaged, is just about upgrade the rotation assembly ( crank and pistons ), and just if whished, one step up camshaft to enjoy the power sensation without loose the driver comfort on street

just my .02 :P

AN if not...

Why not simply rebuild the engine with KB pistons?. They are higher than stock ones so will raise the compresssion a bit. Keep the Magnum camshaft or replace it for something just a bit hotter and done! its time to do it as any other job after all these years. It hasn't to be something to worry or a headache.

You don't want to keep the original bore. It's a lot of work/time/money to remove/replace an engine. If you're going to go through all of that you want to do a rebuild. Fresh everything. The bad part is when you get the engine out, the engine compartment is going to look pretty bad. When these cars were 5 years old there was rust under the battery tray, etc. You're going to start thinking, well if I'm ever going to paint the engine compartment, now's the time to do it. So my advice is before you get started on this project think it over good. Either do it right or continue to drive/enjoy it as you have for the last 30 years.

i have an engine deal worked out for my charger that will come together the first of the year.
i'm with you, rick. i know the engine compartment on my car already looks bad, and to top it off, i covered it with the texaco equivalent of z-bart ! i'm NOT looking forward to cleaning that mess up !

to the OP, if you decide to re-do your engine, at that time, do what you will want to do to the engine compartment [cleaning, restoration, whatever], or just leave everything together as has been mentioned.

Rebuild it properly and run it. Nobody will care that it's been bored out and it will not decrease the value. Stash the original engine and build a different one.... Stupid IMO. Original engine will never make it back into the car if you do that.

So, originality is the most important thing to you. Is this because you like the idea that everything is original in the car AS you drive it around and enjoy it? Or is it that you feel it protects its value by having every original part, in an as close to original condition as possible? If your feeling stems from protecting its originality, pull the motor and either pickle it or disassemble and store it. Buy another 383 and put it in the car to whatever performance you want. Why continue to add wear and tear to the original block. If you like the idea that its totally original AS you drive it you will have to make some compromises. Even if you can get by with a dingle ball hone and a rering/bearing refresh. The bores are just going to continue to wear so at some point it will need to be bored. My car is NOT a highly desireable car. It will never be a high dollar car. With this in mind I decided to store the original 340. Having the original motor IN the car never matter to me, so why not save the wear and tear.

Maybe try to do it using some logic:
Do a compression test to see how the ring and valve seal is.
Check the timing chain to see if it's stretched.
How is the oil pressure?
Is is smoking on startup, compression braking or acceleration?
Does it use oil and how much?
After you have this information we can make informed advice.
Just because the engine has 100,000 miles does not mean it requires rebuilding but it might.

A couple of us are on the same page anyway..

I agree - diagonose the actual condition of the motor. Maybe all it needs is a valve job and a timing chain to bring it back to better performance.

FWIW, cylinder bore wear is not linear. It compounds over miles. For example, if it wore the bore out 100 microns its first 40k miles, it wore the next 100 microns over the next 30k, then the next 20k, etc. So even if the bore is still in spec now, and you hone and re-ring it, you are at the tail end of its potentially useful life and you likely won't get another 100k out of it.

It sounds like you use it as a very causal cruiser. I'd certainly agree with some of the earlier suggestions to go through a good analysis of condition, if its decent then a very thorough tuning procedure to see if that net an increase you are happy with. If it does not and a rebuild is absolutely needed, then based on what you find inside, go with a minimal .010 or .020 overbore to leave as much material as possible.