Yeah, that was my misunderstanding. I "assumed"... and we all know
what that does. I saw what I thought were the source links at the
top of the vbox download page, saw your comment on build essentials,
and didn't keep reading on the vbox site. I appreciate the
clarification, here and above/below.

Interestingly, I didn't know build-essential could be used by
automatically installing bits, so I am glad I was confused, as it is
good to learn!