I don't know for sure, but I distinctly remember that mgr on SunOS was default left handed. Could be the version you had was compiled for right handers.
I think I got mgr source off a free software CD, maybe Walnut Creek brand. I did have to fiddle to get it compiled and working.
I can't find an overall mgr version, that seems to not have been a concept. The entire distribution is on 61 "shar" files, which can be undone even today, 37 years after the code appeared on Usenet:
SOME NOTES ON THE DISTRIBUTION OF MGR AS DONE THROUGH
THE USENET NEWSGROUP COMP.SOURCES.UNIX
--Rich $alz, Thu Nov 17 20:59:01 EST 1988
This is the largest posting to ever appear in comp.sources.unix;
I think it's worth it. Stephen has been very patient about getting
this out. .....
I think I got mgr source off a free software CD, maybe Walnut Creek brand. I did have to fiddle to get it compiled and working.