It is more complicated, tow capability and allowance of baywindows increased during time with improved brakes /and bigger engines. I higghly recommend going through this:
Well what I am thinking of is a Eriba that weighs 800 kgs unloaded with a max gross weight of 1000 kgs. In turn the 1600 single port will be replaced by something about 2100 cc with a uprated gearbox .