Zachariah Allen, b. abt. 1706, son of William Allen and Margaret Waggener, was the elder brother of Erasmus Withers Allen.
Erasmus Withers Allen moved to North Carolina abt. 1770, settling near the fork of the Yadkin river.He lived near his cousin, Samuel Waggener.His eldest daughter, Mary Allen, married John Chapman.John's son, James Chapman married Erasmus Withers Allen's youngest daughter Elizabeth.James Chapman moved close to Erasmus Withers Allen.
All three of these families lived very close to the Bryan and Boone families, Erasmus' property bordering that of William Bryan.
Erasmus had 3 sons (William b. 1741, Streshley b. 1754 and Thomas b. 1756) AND eight daughters.Thomas is believed to have married Margere Bryan and moved with Daniel Boone to KY.There is some evidence that Streshley also moved to KY.I believe some of the Waggener line also moved to KY.Others of Erasmus' line moved to the Cheraw area of SC including son William, b. 1741 and most of the daughters.
Thus, it is most likely the Zachariah Allen you refer to fits into this Allen family in some way.Probably Zachariah Allen, b. 1706 named a son Zachariah b. abt. 1730 and this is the father of Zachariah b. 1754.
Unfortunately, I don't have documented children for Zachariah Allen, b. 1706.It's be nice to bridge the gaps.
Anyone interested in the lineage of Erasmus Withers Allen can find a lot of postings on this GenForum.