i fitted mk3 leather. the back go straight in. just make the bolts on the car longer so they reach the catches. 2 min job the fronbt i took the leather off the base and put it on the base of the mk2 seat. the fit the back of the mk3 seat to the mk2 base. easy job takes about an hour. look like this finished
i put mk3 leather recaros in mine, they look the job and are VERY comfortable... sorry no pics at the mo...
there was a feature car a few years back that mentioned ibiza leather seats going straight in but i never verified this. if a suitable style ibiza ever turned up at my scrappy i was gonna give it a shot.
seat cordoba and ibiza (pre 2000) seats fit a mk2- i had a seat cordoba and put mk2 leather seats in- the back are a bit of a pain tho as the arch space isnt the same- may need to bang new ones in with a hammer!! good luck
my gf's brother had leather rado ones... the back bench in a rado has nice head rests too, i think the front seats go straight in but the back ones need a little bar to hold them in, tkae a look here, ther eis a guid eon how to do it... http://www.matey-matey.com/corrado_seat_conversion.shtml