Well I did some more research and talked to a couple Dodge/Chrysler techs about that grinding noise.

It's not a grinding at all, it's detonating. Now if advancing the timing won't get rid of it, it would mean there's too much carbon in the cylinders and combustion chambers. Now, is there anything else that might cause it?

And if it turns out that it is carbon, what's the best way to get rid of it? I'm familiar with the water trick, but have never really liked that method at all.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Retarding the timing usually reduces or eliminates the pinging. Maybe just buying a better grade of gasoline may help.
If that doesn't help, try a compression test to make sure you don't have a burning valve causing preignition.

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

When I last did a compression test, the compression in the #1 cylinder was really bad. I'll be ajusting the valves today in hopes that they're just out of spec.

Once I can source a later model head I'll do a complete head job and just replace the current one on the engine.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Yes, retard the timing to eliminate detonation. Also, a vacuum leak can cause this problem. Check out your vacuum lines, hoses, power brake booster if applicable.

Run an unlit propane torch around the intake mating surfaces with the engine idling. If it speeds up, it's sucking propane and therefore leaking at that spot.

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It's a Slant thing. Even I don't understand.

1974 Duster, EFI /6 soon to be turbo...

Get that Monkay! Get that nasty thing!!

Mine pinged pretty badly when I got it. Went to check the timing, found the vac adv. had already been disconnected. Only by retarding the timing quite a bit could I eliminate the pinging. Eventually, I went to adjust the rockers; they were at .018/.028 instead of the spec. .010/.020. This adjustment completely eliminated the detonation and allowed me to advance the timing substantially, greatly improving drivability. I eventually figured out that the out of adj. valvetrain had the effect of shortening the cam timing, moving peak cylinder pressure down in the RPM range, and generally creating havoc in the combustion chaimber. FWIW.