My grandfather is Oliver Gerald (O.G.) Engquist. He is originally from Nebraska. His father Swan Peter (S.P.) Engquist came over here from Sweeden. I believe he did change the last name. I'm not sure what from. (I'll have to ask my Grandmother.)
I don't know if this is even the same Engquist you're looking for. It's not a common last name, so I wanted to post something for you. If I can help you in your search, please let me know.