Yes.

Nobody knows the answer to your question.

It doesn't help that you haven't specified which TDI, could be 90, 110, 130 or 150 bhp, the last two being PD.

My owners manual doesn't have information for the 20vT engine, only the normally aspirated. And its a Toledo, so no help for comparison with a Leon.

The owners manual has kerb weight figures. Maybe someone with 20vT and TDI Leon's will give you those figures. Bare weights for engine and gearbox, though, will be hard to find.
 
Leon owners manual in pdf format listed here shows the following:

1.8 20V 92 kW petrol engine
Free standing weight in driving order in kg 1321

1.8 20VT 132 kW (6-speed) petrol engine
Free standing weight in driving order in kg 1364

1.9 TDI 110 kW (6-speed) Diesel engine
Free standing weight in driving order in kg 1390

1.9 TDI 96 kW Diesel engine
Free standing weight in driving order in kg 1368

1.9 TDI 81 kW Diesel engine
Free standing weight in driving order in kg 1334
 
SHADY-NINJA wrote

the car is a seat leon cupra 1.820vt
Cupra not LCR, then it's the 132 kW (180BHP) car at 1364 kilos

while the diesel is a seat leon 1.9 tdi cupra
which is the 110kW (150BHP) car, at 1390 kilos.

36 kilos difference, 4 stones or 56 pounds. Weight of a small child.
 
Its less than that its 26 kilos (sorry to correct your maths)

Take in to account the petrol Cupra will have larger front discs and I believe a slightly thicker ARB so there is probably a couple of Kilos there.

All in all there is not much difference at all.