There wouldn't be any extra torque.
The MK2 8v is only a 1.8 litre - but the MK3 8v block happily fits under the MK2 head. The reason MK2 owners keep their MK2 head, is so that they can retain the existing engine management, without needing to change it to MK3 management.
Ie. For me, if I was to do it, I have a mechanical injection 8v (no ECU), I have two choices, bolt on the MK3 block and get a 2.0 8v, or I take the entire MK3 engine and then have to fit the full MK3 loom, ECU and ancillaries.
The reason we keep the head is for convenience, not a huge amount else.
Get yourself a lairy cam, free-er flowing exhaust and performance panel filter and you'll free up a few ponys without it being 'too obvious'