They were always bolt on necks. The Pro, MkI and MkII models were 4-bolt with a conventional neck plate. Once the MkIII came out, that model has the contoured heel with countersunk neck bolts, which could have been ordered on a MkII during the Pete era. Not known if Paul will do it now.
You can also see the necks are laminate construction. In the old days it was 2pc hornbeam in the center section. When Wal ran out of hornbeam around Y2K, maple went in the center section.