New cams that open and close the valves at the right time would be needed. Starter that starts the other way. Probably a dry sump because the normal sump would pump oil the wrong way and you'd have no pressure, likewise PAS for same reason. Alternator wouldn't work backwards, the regulator would stop it putting anything out I think but that's easy to swap for another. Water pump - I'd pull the impeller off and fit a opposite one, freely available and bearing shafts are standard sizes. Then map it I reckon.
Two suggestions for next time though:
1) Use an S2000 engine. The money you saved you spent on getting it to run the other way.
2) Turn the rear diff upside down. But the gearbox might die running backwards. So go with 1)