4.5 l
If the flywheel from a 6 liter and related parts mount, but from the factory neither ford or international offers a manual. Also I don't know how integrated the transmission control is to the engine control. If you have access to a donor truck with all the parts there including the engine, chassis, and transmission harness it might be worth a try.
Before you get that far I should tell you that I have seen broken intake elbows, cracked flexplates, bad injectors on engines just 1 year old. It could be an interesting if complicated swap. Keep us posted on your progress.