Well, my luck didn't hold. The researcher looked for every McKee in the Mount/Port Norris area that was born in the 1820s. He found a few but none are my Alexander or any other of the McKee family members I'm looking for. Here are results from the researcher.
I've sent a follow up question to the researcher. Based on church history for the Mount/Port Norris area, Presbyterians were going to church at Markethill. Since a record of Alexander's older brother Robert shows a place of birth as County Armagh, I've asked the researcher if looking at Markethill is a reasonable next step. I've also asked the researcher to suggest an alternative search if he has a suggestion.
I'll keep posting as long as I have questions, options, the attention of the researcher, and disposable cash.