The certification would be the responsibility of the country of registration. As far as the CAA is concerned a Type (ie one of a series) certificate was issued 13th June 1969 (ARB ref FA3) The variant D4 was added as this was the only variant on the UK register. The -0 and the -J models were never added. There is only one CL44-0 variant, it is unique, so it could hardly be regarded as a supplemental 'Type' anyway, whereas the Belfast is a Series Type in its own right, a military aircraft that was 'civilized'.
I would think that CAP733 Permit to Fly, para 1.3, would cover the Guppy's present situation.