Loren, thank you again. This is all very interesting. It would seem that if what you state is true, then:
1) Alonzo's father was David.
2) David must be a son of Reuben because of the date of his marriage (~1797/98) compared with the dates of marriage of the other two brothers (Seymour ~1803 and John ~1805).
3) David would probably have been Reuben's and Mary's first born in order for him to have fathered Alonzo in 1820/21. (Of course if Alonzo's date of birth was later, then this theory is no good. I have seen Alonzo's date of birth also listed between 1820 and 1825), so ???
4) This would make my theory that Benjamin was not Alonzo's GF, but his GGF more realistic.
5) What would tie this together somewhat, would be to find David's date of death. If it is late 1850 or early 1851 than he would more than likely be Alonzo's father, since Alonzo claimed in a letter written in April of 1851 that his father had recently passed away.