To prove that Levi Rolf Stafford is the father of Lealdus with autosomal DNA will be very tricky. Beyond your immediate couple of generations, DNA offers supportive evidence to the paper trail, but not proof.
First, you'll need to have DNA matches that you're related to that are descended from Levi Rolf Stafford - this also needs to be proven by using traditional paper research.
The matches need to be fairly strong and not the result of simple random recombination. Ideally you and your matches should share DNA on the same chromosome in the same "slot", and you all share a reasonable amount of DNA over-all (say > 10cm).
Then, the ancestry of both yourself and your matches needs to be researched the paper way to prove that you're not related in any other possible way.
Once you've established that the only possible way you share DNA with your matches is through Lealdus' father, then you can be sure that whomever the paper research has shown to be his father, is supported by DNA.
You would be in a better position if you have a set of male-line descendants tested. Thus, if you can trace a line of sons from Lealdus's father, and match the Y-dna up between those individuals, then that could be used with proof. If your cousin is a male-line descendant of Lealdus' father, then certainly it would help - and if you have a brother, or can get your father or an uncle to test, then that would also be very useful. Then, of course, you'll need the matches from a different branch of Lealdus's father's family and the associated paper research to corroborate the match. To test Y-DNA for males like this should most likely be done to quite a high level, at 111 markers or more.
