For one thing your dates may be a bit mixed up. Ancestry has a marriage record for James Kerr & Rowan Spear in 1733. They also have immigration records. She came here in 1732 so they married in the US. Unless he left and came back he could not have immigrated in 1734 "after" they married. It had to be 1733 or before. There is an immigration record for him from an index but it does not specify the year. The port for both was Pennsylvania.

I am a descendant. I question though if this is "my" James Kerr as my dna shows no Scottish blood what-so-ever. Of course he could have lived in Scotland but not been Scottish.