Hi,
The support of SunOS 4.1.3 seems to be available in gs-gnu-5.50a (read
the Make.html file in the doc before) and after. The last version have
always a notice about make gs in SunOS environment but they haven't
tested this plateform.
Maybe you can try the 5.50a version ?
Best Regards
Didier Link
GNU Ghostscript maintainer