UM10.6 non-GRIB start dump

Hi CMS Helpdesk:
I have made progress in upgrading my suite from a 10.6 UM branch that works on MONSOON to a 10.7 UM branch (and eventually to a 11.5 UM branch) that works on ARCHER2, and I have now encountered the same message that Markus Todt @mtodt encountered a couple of years ago:

I don’t have access to the Met Office supercomputer, so I can’t see if there are non-GRIB versions of this 1950 start dump there in the same or similar directory as this is located in: /data/d05/hadom/startdumps/era20c_1950010100.grib

Can you please check if such a file exists or not?
Also, is there a GRIB API available (on ARCHER2)?

On advice by email from the CMS Helpdesk, I am currently trying to use the (non-GRIB) dump from the beginning of 1951 from the suite run on the Met Office supercomputer (that suite was run, starting with the 19500101 GRIB startdump). This non-GRIB dump was found on moose. There wasn’t a 19500101 startdump available on moose (right after recon from the 19500101 GRIB start dump).