I also reset the gear linkage whilst i was under the car, but this can be done above the car. All you need is a 5mm steel dowel / nail / punch pin / drill bit. But wrap some tape around the end to make sure it does not drop down into the selector housing.
I bought a 5mm brass dowel from ebay for £2 and heated it up to create a kink to ensure it was not going to drop through.
Great video on youtube as below.
Lock gearbox first, then open up selector springs, then pin the gearstick and tension selector springs, now unlock gearbox and in-pin gearstick = nice positive selection of gears