There is, in North America, a build sticker under the carpet in the trunk / boot / cargo area. That sticker lists the equipment installed at the time of manufacture. The engine code, as assembled, would be listed.
I can't rule out that the engine might have been swapped sometime in the prior 25 years.
The 110 and 130 hp TDI that were available in other markets might look identical externally to the 90 hp ALH version of the 1.9.