> ld: warning: sparc:v9 architecture of input file `/sys/arch/sparc64/compile/NONPLUS/lib/compat/libcompat.a(tty_43.o)' is incompatible with sparc output

You are supposed to use a sparc (not sparc64) compiler to build 32bit kernels.
You can create one with (from memory, not tested)

  cd /usr/src && ./build.sh -m sparc -a sparc -t

and then using ${TOOLDIR}/bin/nbmake-sparc instead of "make" when compiling
a kernel.

Martin

P.S.: I tried this some weeks ago and got the machine up & running, but 
couldn't compile basic pkgs from pkgsrc (pkgtools/digest failed). At that
time I blamed that to kernel bugs, but didn't investigate further.