Why don;t you mod the golf?
It will be less effort and less expensive.
Make then the Bakkie your daily driver.

If not then:

You must get hold of the Toyota cressida gearbox. Then buy a adapter bellhousing to make it fit the motor. I think you will have to remove the nissan tunnel gearbox mountings and make a custom gearbox x-member to bolt it through the floor.
There is pictures on this site on how to do this professionally.
The cressida gearbox is nice and strong.
Also I do not know about the clutch assembly on what you will need to do there and if the clutch will work together because you will now use a different gearbox that the engine did not come with.
You must then also be careful with your brakes. The 1400 bakkie brakes will not perform very well with high speed braking.
It will start to brake fade after a short while.

Talk to the local drag racers. Most of them will have done this mod to their 1400's and will be able to assist you. Theirs will however have BIG turbos on and yours will be N/A.
It will definately rock for a N/A bakkie.
N/A, that is what I like.