OK I have answered my own question but the information may be of help to others. the reason I could not fit the new Walbro pump is because in their wisdom Saab had a change over in 1998.
This is not indicated by the chassis number only the pump model# 5601. cure, purchase a new type pump complete with housing etc at a cost of £300
This is not indicated by the chassis number only the pump model# 5601. cure, purchase a new type pump complete with housing etc at a cost of £300