It seems I spoke too soon... The NFS share is visible in that ls shows its contents but copying to or from it from the DSL client hardly works.
To get to this stage I have installed DSL 4.4.10, modified /etc/init.d/S99bootlocal to include the lines:
5 pump -i eth0
6 /etc/init.d/ssh start
7 /etc/init.d/portmap start
8 /etc/init.d/nfs-common start
The share is mounted with mount -t nfs server:/path/to/server/share /mnt/dsl/share
I see during startup that this all works without producing error messages, and as I said the share is visible but when I try to copy files from the server share to the DSL local disk the first 16Kb copies OK, then the copy freezes.
I've Googled a bit but found nothing, any clues anyone?