I’m happy to report that I only had to make on adjustment to the 11g client in order to make it available to my customers.  The 751 permissions on sqlplus continue to result in

map : Permission Denied

errors by users who aren’t in the DBA group, but while this was mostly an annoyance in 10g, in 11g it resulted in a fault and a core dump.  Setting the permission to 755 cleared the problem.  Thank goodness I wrote that post back in May.  When I Googled the error, I got my own post!