Linux NFS Compatability With SVR[34]

I still have a couple of dinosaurs running SVR3 and SVR4. Trying to
mount a share from a Linux server. Mount succeeded and no errors in
Linux syslog however, when I attempt to access the mounted resource on
the old machine, my shell is frozen (no tty control) - can't kill it,
etc. I had this working previously but it's been some years ago -
likely with the 1.2 series kernel (old Slackware). Seems that there was
some effort involved in getting it to work but for the life of me don't
recall what it took. I've tried both 2.6.5 kernel nfs and userland
daemons - no dice.

Anyone have any idea what the issue may be?

Thanks.