Dog One. At AN when a new type was introduced the initial crews were sourced from numerous types. When the DC9 was introduced the initial school of 20 pilots consisted of mainly Viscount and DC6B pilots plus a small number of L188 pilots and at least one B727 pilot from memory.
(This was the era when AN accepted 19 year olds with a bare CPL, < 200 hours of SE time and no Instrument Rating).