The chassis might be the same, but the diesel ones are reinforced. I dunno for Fabia, but for other cars are special kits for petrol to diesel conversion.

So, not the same then?

Naturally! Diesel powered cars have reinforced chassis/frames/engine mounts and so on. They need to handle that extra torque and vibrations that a petrol car wouldn't develop and it wouldn't need. Fitting a petrol car the same parts as for a diesel one would be a total waste of weight.

Tdi to vRS conversion is not simple. Just modify the tdi engine. They will take a lot.