ratio's differ, spec's are on the um, spec's page, and/or detailed in the manuals.
as a result of the differing ratio's i'd guess you need a complete H or a complete L and wouldnt be able to mix n match, but i may be wrong, i dont really "do" gearboxes.
As far as im aware the shafts can be changed between the to engines but as zimm said you dont want to mix and match you need both shafts to be from the same model,
Dont take my word for it though because i dont know for sure i have had both engines apart and they look the same but iv never tried to change the boxes between models