has any one done an 2.0 engine swap with a golf mk3 in to a 6n

it wont fit cos its a tall block, you could make it fit if you had loadsa money, but if your gonna spend loads of money it wouldnt be the engine i would use. vr6 and 1.8t seem to be the popular ones if you have money to burn!

How much difference is there between a seat ibiza 2.0 16v ABF and a mk4 polo under the bonnet?

I thought that the newer ibizas were quite similar or are they still a mk2 golf?

Although the Ibiza and the 6N polo are pretty much the same car, the one significant difference is the size of the engine bay. Ibizas come with much larger engine bays which can acommodate the big block engines, whereas the polo 6N's all have small block engines. The only polo with an easy capacity for a big block is the saloon/estate, because basically that is a cordoba (Ibiza with a boot) with diferent badges and slightly different rear styling. That's why the 1.6 polo saloon is 100bhp instead of th 75bhp in the polo hatchback 1.6 - because it's a big block.

Mind you, I saw a saloon decked on diamond cut TT alloys on here last year, think it was in south africa, and it looked PIMP.