Swapping 5 speeder for 4 speeder

anyone any comment on if this is possible? I'd naturally assume you would need the gearbox ECU as well but other than that is it a major piece of work to swap from a 4.2 early 4 speeder into a 4.2 '97 5 speeder?

From the post that suggests the 4 speeder is robust enough that its covering huge mileage without concern I'd be happy to trade a little performance hit for piece of mind that my gearbox isn't about to blow up every two mins.