> Now, as I've got all sources and lots of free cpu-cycles, I want to try to
> build 060-optimized system-binaries.
[...]
> I've got all sources extracted to /usr/src, what now?

The kernel will probably build with -m68060 flag already set.
If you want to compile all binaries with -m68060 add the following line
to /etc/mk.conf:

COPTS = -m68060

or modify /usr/share/mk/sys.mk
CFLAGS = -O2 -m68060

If you would like to compile X-Windows for 68060, modify:
/usr/xsrc/xc/config/cf/NetBSD.cf

	regards

		- Adam