Well...
Whenever I pull an exhaust, I replace the hardware with non-ferrous alloy, to prevent galling and heat siezure. Brass will work nicely (if you can find hex caps or socket heads easily enough,) but I usually end up getting silicon bronze from Fastenal. Retain the steel Belleville spring washers (the little dishes,) as they spread clamping force and promote sealing.
For a threadlocker, I use LocTite #272. It is designed for high heat applications, and it is fairly common for the long manifolds on the I6 to work loose over time without a little help (I've seen this on Big 3 iron as well - it's not peculiar to the AMC six.) You may have to do some looking to find it, but it's worth the effort IMO.
5-90