The Ford linkages have a hole to put a pin through to lock the stick in position, I can't remember what gear.

But all I did was put the box in 4th, loosen the linkage, get a mate inside the car to hold the stick where I wanted 4th to be, then tighten the linkage.

It's very very likely to be just a linkage adjustment problem, but I've seen rebuilt gearboxes that were junk