Torque them properly and they shouldn't come out. Does it use a gasket? If the gasket is 'soft' or deteriorated then the threads lose tension.
Showed you what AMC did. Chrysler obviously didn't find it neccessary or they would have done the same or similar.
For $$ you should still be able to buy Spiralock made by Detroit Tool. Its a slightly better thread form, closer to Whitworth in cross section, designed for the purpose of preventing threads from backing out. I'd only do that if you continue to have problems.