Is a '69 AMX considered a mopar A-body?

Well, to the OP, since you mentioned it, what you should be r can do with it is your call but IF I had the spare coin, I would....
(Enter evil laugh here.....)

Get an aluminum Indy block and heads, stroke that sucker to the max with there max ported heads and make Ford and Chevy guys cry all night and run in fear all day.

I have said this a bunch before, IF an AMC challenges you, be prepared to have your clock cleaned. IF they know what there doing, it’ll run!