Can I fit 3 point seat belts in a Mexican VW beetle?

I have been told that it is a fairly simple job to mount a 3 point seat belt in the rear of a VW Beetle.

But when I went to the garage to get this done I was told that because I am driving a 1985 mexican import, this can be done but it is a much bigger task involving taking out the headlining (and most likely ripping it!) and reinforcing the pillar or something to accommodate the brackets etc.

Is there actually a provision in the German built Beetles that allows rear 3 point seat belts to be fitted easier than in a Mexican built one? (This is what the garage leads me to believe)

Or is this garage trying to pull the wool over my eyes!?