1.6TD - cheapest of the vw turbo diesel options, tunable, reliable, enough balls when tuned. i would steer clear of turboing the NA 1.6 unless you plan to work in oil squirters somehow...or keep the boost really low and your eye on an EGT gauge.
1.6TD should fall right in there with minimal fuss. items you will have to change... airbox, downpipe, possibly fuel filter mounting but i'm not sure on a mkII.... as far as electronics and sensors go... it should be a breeze.
1.6TD