The 1.3 piston is taller than the 1.6 so if you want a high comp 1.6 retain the 1.3 piston and mix with 1.6 conrod and take the crank from CPS This setup you IINM you can only run high ron fuel. The other you can do is swap in the 1.6 parts including the piston. I have friends who's running 1.6 internal and running full standalone on his BLM. Piggyback cannot use on BLM one the factory ECU is lock and it will overwrite the piggyback mapping when you off and restart back the car.
Or he can just go hunt for CPS and swap it in. The block on CPS is the same. Is the cylinder head different and the intake system different.
He can choose to retain the 1.3 internal and mod the bolt on parts. Power wise I think should be ok. If the car is not broken don't fix it.
Cylinder Bore on 1.3 and 1.6 is the same at 76mm, stroke on 1.3 is 73.6mm and 1.6 is 88mm.