My advice, fix that 1600cm3 engine ! The only advantage of the 1300cm3 engine is that it's a silent engine due to having the distribution on belt ! Don't forget, you car has a 1:3.9 differential, the 1500cm3 has 1:4.1 and the 1200-1300 has 1:4.3 ! So, practically, because of your gearbox, witch has slighter different ratios, and because of the differential, you will have almoast no acceleration with this engine :P