another stupid question

Hi,

I found a site that has a NetBSD 4 release binaries that have been
compiled with processor optimization and although I could do this myself,
this will save me alot of time. Where I have a problem is that I need to
build a custom kernel and I don't think that a generic kernel will work. I
should be able to download the source, but now that I went to
ftp.netbsd.org. I found NetBSD-4.0 and NetBSD-release-4-0. So, when I went
to the website and did a search, I found that NetBSD release was done on
Dec. 17. I thought that would help me determine which one to use, but
NetBSD-4.0 directories have a date of Dec.  16 and NetBSD-release-4-0 has
much newer dates. I was going to use the source from the NetBSD-4.0
directory. I might be missing the obvious, but do I need the exact same
source from the exact same date to build a proper custom kernel for the
userland that I downloaded?

Thanks,
Al