I'd snoop around delta and see if you can find out more. They used to hire machinist's helpers who would learn to run CNG stuff at a tech school on the side. They have an engine shop in the old northwest hangar now-in addition to the big tech ops center. Lots of guys got skills working on engines and such-and that makes them very valuable to engine manufacturers and airlines.
I know a guy that works at Delta right now that hired in as a store keeper about 4 years ago became a mechanics helper and now is an A&P in the hangar.
If you can get in they will train you.