Monroe was the OEM supplier for Chrysler in those years. The shocks had "MAECO" stamped on them, rather than "Monroe". "MAECO" = Monroe Auto Equipment Company.
The front shocks are limited due to the tube in the k-frame they must be in, so they were all 1" bore shocks, even HD. As the rear shocks were std 1", with HD being larger in diameter.
When it was time for shocks on the '66 Newport Town Sedan, I talked my parents into the factory HD replacement shocks. They did good, but ended up putting Gabriel Striders on the front. They had three levels of stiffness, adjustable. At the base setting, they were a little stiffer than the Chrysler HD shocks. When they got a little wear, they went to the middle adjustment. It was quite a good shock! Road firm and the car liked them.
A "shock" is not a "shock", per se. Different brands have different valving and ride differently as a result. KYBs are a mid-pressure gas shock. Bilsteins are a high-pressure gas shock. Other gas shocks are low-pressure. Just don't cut the cord before the shock in in place on the car!
Another observed issue is that some brands will have rear shocks, but no front ones in their catalog. For a default shock, the MonroMatics might be a good choice. Might even have the original OEM valving? Then would be the KYBs, which usually have good reviews for Chrysler products. The ultimate would be Konis. It's said that the company owner drove Chryslers and their Chrysler listings were the best there was. Plus the adjustability factor and a lifetime warranty that works . . . as long as vermits don't shread the sales invoice you were saving.
One other thing I found out is that tire choice is important to how the shock works. On my '77 Camaro, I had some Pirelli P77s on it and could never get the Konis adjusted to feel right. Kept adjusting and such, even waiting a few thousand miles to adjust them, to no avail. The rubber and construction on those radials were apparently filtering the little things out so the shocks felt they were on glass-smooth Interstates when they weren't, so the valving never stiffened up for dips, bumps, or whatever. When I put Radial T/As on it, things felt better again! The BFGs had a stiffer sidewall and that gutsy feeling returned.
So do your research online, starting possibly at RockAuto, in general, and the Monroe or KYB or Koni websites in particular. That'll give you a sense of what's available and at what price. The shockwarehouse website would be good to look at too.
CBODY67