Thanks for all replies and suggestions

Using a oxy-acetylene torch to set the carbon deposits on fire, and then using only the oxygen stream to encourage it to burn on through the passages is interesting, but as other have said, on an aluminum manifold mounted on the engine I think I should be more cautious on the first attempt.
{my mind brings up the image of how the aluminum British ship Sheffield burned when hit by a Exocet missile years ago}

What I did last night on my 1995 Magnum 5.9V8 EGR passages was this:

First I checked for a blown belly pan gasket by taping up the PCV, Breather and Oil Filler Cap openings in the valve covers.
I taped into the oil filter opening one end of about 8 feet of clear plastic tubing and filled the other end of the tubing with about 2 feet of water to make a rough manometer.
My fully warmed up engine showed about 3 inches of positive pressure from the blow-by at idle, with all the taped openings 'pouching out' as well, so no sign of vacuum, like you would get from a blown bellypan gasket, although mine is original factory.
I then took off the air cleaner and stuck a 1 inch wide by 2 inch long mirror down the throttle opening and looked around and found nothing looking bad at the gasket line inside the manifold.

From a Formula 409 household cleaner spray bottle I took the hard but flexible small diameter plastic tube off the suction part inside, and bent this tube into a snake-like "S" shape so that I could guide it into the outlet of the EGR passage deep down in the intake manifold.
I pulled the spray cap off the Chrysler Combustion Chamber Cleaner spraycan and found a length of black rubber tubing that came with a hand held vacuum pump kit to connect the CCCC spraycan outlet tip directly to my makeshift snake tubing running down into the intake manifold. I put about half the contents of the CCCC down into outlet of the EGR this way.
It took three tries before getting the tubing deep enough into the EGR passageway to keep the CCCC foam from backing out the other EGR outlet just under the other throttle bore.

I then let this fluid put in the EGR outlet sit about an hour before starting the engine, while I put the rest of the CCCC spraycan contents into the port on the EGR valve for sensing exhaust backpressure. I used a longer length of black rubber vacuum tubing to reach this small steel pipe nipple near the firewall. Since the EGR valve was closed I figured most of this CCCC foam would go down the steel tube toward the exhaust manifold on the passenger side of the engine compartment. This got to sit about 30 minutes.

I hooked up a hand operated vacuum pump to the bellows on the EGR valve just before starting the engine, but did not apply any vacuum at first.

The engine started up a little hard with the CCCC in the passages, but got going with a few stumbles and then held a pretty reasonable idle. I let it idle about 5 minutes before slowly applying some vacuum with the hand pump to the EGR. When the vacuum level got to 6 inches of Hg the engine stumbled and almost died, but recovered and held a rough idle. With the air cleaner housing off I think I could hear the noise of stuff running through the EGR passageways and hitting the outside aluminum walls of the manifold.

Lots of dark smoke began to come out of the tailpipe, enough that I had to yell
'Sorry' to some neighbors walking past the house.
They smiled and yelled back:
"Looks really bad, do you think you can fix it?"
I yelled back 'Yes'
and they yelled back:
"Have your heard about that new Cash for Clunkers law that just passed?"
LOL

It took about 10 minutes for the smoke to begin go away.

I raised the rpm to 2000 a few times,
and increased the vacuum on the EGR valve bellows to as much as 18 inches Hg.
To my surprise the engine would idle with that much EGR flowing but the engine was really rough and sounded like it was missing every third or fourth beat.

I experimented a bit.
With EGR turned off the engine was using its normal 0.7 gallons per hour at idle, as measured by an Oztrip aftermarket trip computer.
With the EGR flowing with vacuum on the bellows at about 10 inches Hg, the engine needed 1.0 gallons per hour to do a rough idle.

I am fairly confident that this cleaned up the EGR passages.
Certainly some EGR is flowing because of how the engine idle becomes so rough when the vacuum is applied to the EGR valve bellows, and also the old (15 yrs, 200,000 miles) EGR pintle valve & seat must still be operating,
although it is hard to know if it is allowing some small leakage all the time.

I have a brand new Chrysler EGR valve, and may put it on, but I may frist drill and tap a quarter inch diameter pipe fitting hole on this new EGR valve into the outlet side port area before installing it. This extra port would make it really easy to get flush fluid like Chrysler Combustion Chamber Cleaner into the system.... much easier than snaking a tube down the throttle bores to the EGR outlets.

I have been reading about 'Cooled EGR' on many of the new diesels, but also on the revised design Toyota Tundra gasoline 4.6L V8.
During this clean-out I got to thinking about whether cooled EGR would be a good or bad thing on my old engine. It would not be that hard to cool the EGR gases by running pipe up to the radiator area and back. Another simple way would be to make use of the natural cooling in the existing exhaust system, by taping into the exhaust back behind the muffler and running a line forward. The EGR gases would cool going backward and then forward.

While I am fairly confident cooled EGR would reduce NOx,
I am not sure in my mind whether it would improve MPG,
although my current understanding is that more and more EGR flow reduces 'pumping loss' and improves part-throttle engine efficiency ... but only up to the point that all that charge dilution begins causing ignition missfires and very slow burn speeds.
Cooled EGR would not heat up the incoming fresh air charge as much during part-throttle highway cruise, which might allow the partially throttled engine to produce enough added torque that it would climb a little bit steeper highway hill without a downshift.