Accurate makes them too, they might be able to help.........

http://www.accurateltd.com/E-Body-HP-Mufflers-Turn-Down-Date-Coded-688HP-TD-689HP-TD_p_229.html

Great pictures Earl!
I'll dig a couple NOS ones out of the bus for some close-up shots later.
There were two different style rear brackets used as stated and two different style tips...oops this is the front.

Here's the rear shot

557 turn down tip with the early style bracket..

with a good 8-70 date..

later style bracket..

most with this bracket had 72-74 dates..

You still have a bunch - Another hold-out from my Buddy!

WOW

That's a crazy pile of mufflers - you might have to help a California guy out

You are still my Buddy!

Couldn't they be lightly glass beaded then coated with some sort of temp coating?

Absolutely not.. they are JUNK...
please send to my shop for proper disposal...

The 'issues' I was speaking of are, although still brand new most have had some repair.
The place that has them, for years in the early 60's into the 70's had a contract with Chrysler to remove certain items from their Mississsauga Depot after they were obsoleted from their system.
Chrysler had their depot people punch a few holes in them and sold them as scrap. Not all them got punched with the icepick probably due to lazy employees which was a good thing in the long run.
But those ones were the first to get picked and are long gone.
This place brazed the holes and over the years sold plenty of them or installed them as a used part on customer cars since they are a garage also.
These are what are left from 40 pair, and passenger side only are all that remain.
The following photos show the repair.
Some are high enough up on the side or top so as not to be seen when installed.

another one..

In the early 80's when I first found these, They also had 30 pair of the 3404557-8 tip style, clean, and untouched by the icepick, correct for 340,383, 440 and 426.
I grabbed those first and believe it or not couldn't give them away at the Mopar Nats then at $200.00 a pair.
How times change...The last few pair went several years back on Nats OE destined E-bodies.

ends..

Mccannix I think the muffler third down on the right is now on my Challenger Convertable.It did not have the filled in holes. I think I still have one side 1971 date coded turn down muffler. Since I now work afternoons two weeks out of the month, maybe you and I could take a road trip again and take a look at that stuff one more time.

I'm always up for a road trip...