Another thing to consider about the additional weight isn't so much it's even distribution, but surely where that weight appears dynamically.
The greater proportion of the additional weight will end up being transferred onto the outside front tyre in a corner. You're now chucking an extra 75kg+ into a bit of rubber less than the size of a 1/4 of a sheet of A4 paper. Even if you reduce the tyre wall to reduce lateral shift in the load its an awful lot more it has to deal with and keep planted to the tarmac. The rear suspension may help the turn in but it's still that front tyre carrying much of the additional load and getting you around the corner. Same size tyre (not sure whats fitted to the various cars but I suspect they're all around 225 wide) means it's ultimately going to complain or give way earlier on an heavier 3.0L than a 1.9. Getting more or stickier rubber will help.
Sit 4 x 56Ib bags of potatoes on the bonnet of your 1.9 and see how it reacts then!