Accessing a legacy NFS

I have an old headless box running Caldera Linux from 1990s. There is no SSH in Caldera. The box has no USB or other ways to add a portable drive. Years ago, I had similar Linux boxes and I used NFS to back up. My other boxes have become more modern and I have not made a back up of the Caldera box in years. I’m feeling a bit insecure. Via telnet, I use the box regularly and add data.

I was considering pulling the drives out temporarily and turning them into USB drives. But, right now, I’m trying NFS again. Over the years, I’ve tried to mount the Caldera on a more modern Debian/Ubuntu/Mint box. In every case, I’ve failed and put the project aside as not urgent.

I’ve just done done a fresh Mint 19 install just to pursue this problem. For naught:

root@willie-Latitude-E6420:/mnt# mount -t nfs 192.168.110.16:/ /mnt/bookkeep
mount.nfs: Protocol not supported

Can anyone offer any insight on the incompatibilities in NFS that have been introduced over the years as "improvements"? Can anyone suggest a distribution that might support old NFS mounts? Or other work arounds?

rpcinfo -p bookkeep
   program vers proto   port  service
    100000    2   tcp    111  portmapper
    100000    2   udp    111  portmapper
    300019    1   udp    731  amd
    100005    1   udp    766  mountd
    100005    2   udp    766  mountd
    100005    1   tcp    769  mountd
    100005    2   tcp    769  mountd
    100003    2   udp   2049  nfs
    100003    2   tcp   2049  nfs
    100001   13   udp    780  rstatd
    100001    3   udp    780  rstatd
    100001    2   udp    780  rstatd
    100001    1   udp    780  rstatd
    100001   13   tcp    785  rstatd
    100001    3   tcp    785  rstatd
    100001    2   tcp    785  rstatd
    100001    1   tcp    785  rstatd

rpcinfo -p localhost
   program vers proto   port  service
    100000    4   tcp    111  portmapper
    100000    3   tcp    111  portmapper
    100000    2   tcp    111  portmapper
    100000    4   udp    111  portmapper
    100000    3   udp    111  portmapper
    100000    2   udp    111  portmapper
    100005    1   udp  53399  mountd
    100005    1   tcp  46155  mountd
    100005    2   udp  49673  mountd
    100005    2   tcp  47513  mountd
    100005    3   udp  42853  mountd
    100005    3   tcp  54595  mountd
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100227    3   tcp   2049
    100003    3   udp   2049  nfs
    100227    3   udp   2049
    100021    1   udp  34963  nlockmgr
    100021    3   udp  34963  nlockmgr
    100021    4   udp  34963  nlockmgr
    100021    1   tcp  46437  nlockmgr
    100021    3   tcp  46437  nlockmgr
    100021    4   tcp  46437  nlockmgr

rpcinfo -p bookkeep
   program vers proto   port  service
    100003    2   udp   2049  nfs
    100003    2   tcp   2049  nfs

mount -t nfs -o vers=2 bookkeep:/ /mnt/bookkeep