How can I copy into the Mac clipboard from vim?

x11 isn't needed for copying to the clipboard since mac doesn't use x11. Recompile vim without x11. My guess is that you are copying to the x11 clipboard which you don't know how to access from the mac side.

In macports using the huge variant is sufficient to get clipboard support working.

port install vim +huge

From memory in Vim you can use pbcopy and pbpaste the same way as any other external command. To copy the current line to the clipboard type:

:.!pbcopy

to copy lines 1 to 50

:1,50!pbcopy

To copy the contents of the clipboard into the current vim bufer use:

:r !pbpaste