Did you swap all the ancillaries?I've had this before with that very engine,a totally seized alternator causing the v belt to jam up.it could be something easy like that,I cut the belt and it fired instantly but changing the alternator was a pig of a job,didn't help mine had aircon!!!

Iirc there is a pulley system between the alternator and the belts and pulleys which is held on the coupling with three bolts meaning you could just undo them and try it?