1973 DT3.  It seems like somewhere I read in a post that for a two prong flasher you don't need a ground and two prong flasher will work, Maybe I imagined this, but just two prongs, no place to put a ground. Will the two prong work?

Just put a Napa #535 2 prong in mine with no problems.

Yes, 2 prong is correct and what you need unless you're using the original equipment flasher. 

(Modern 3 prong has a second "output" wire and not a ground so you'd end up with a direct short if you connect the 3rd terminal of a modern flasher to ground.)