this is how I modified some porsche seats to fit a mk2/3 polo. its should be similar for mk4's as they are a similar design to the earlier models, just the rails that the slide in are wider apart.

First take an old polo seat and strip it to the frame

tack weld a steel strip between the bottom of the rear two seat runners so that they are kept the same distance apart.

next cut the bottom of the rear legs off the polo seats (with the metal bar welded to them)

next weld some square tubing across the sliders for the porsche seats so that the front leg of the polo seat can be welded to it (the front leg isnt welded in place yet)

then weld the polos rear legs to the porsche seat runners (the lump of wood on the sqaure tube that was welded on earlier is to keep the alignment of the rear legs in the right place

next cut the adjusting rail off the polo seat and weld it onto the porsche seat. it can be shorter than normal as the sliders on the porsche seat can be used instead.

and one modified porsche seat to fit a polo

if you want to do this you'll have to work out the dimensions yourself as I've forgotten them

Thankx for doing that, i spose thats helped a little. ile maybe just show these pics to a local welder that I'm friends with and he may be able to go from there?