I was thinking not stock for early ‘63, but then I look at your intake manifold which is where typically the large stock oil filter unit mounted, but no mount holes. Realized you showed earlier that this manifold has an FJ25 part number, which I also thought was no big deal for an early ‘63, but maybe the manifold is also not stock for this rig. So basically I have no clue, .
More looking... air cleaner mount location on head, that‘s also FJ25ish. Is this the original motor (s/n matches tag on firewall)? Maybe there are lot of parallels between the 25s and the early 45s.