hi...
basically getting a perfect setup is not an easy job...
till now even myself, is not satisfied with my setup....
ok lets get to ur Q? an example... ur car is originally an iswara with 1.3 engine then u convert it to say...a 4g61 engine...the weight is very much different. therefore u need to get a higher rate of damper to accomodate higher rate springs.
but when u talk about just changing the head fm single to twin cam...weight factor is not really an issue.... guess u are reffering to handling issues now, so there is always a compromise when it comes to this. better handling would sacrifice comfort...take example car is used for daily commuting....(highways, sweeping roads, road bumps etc) i'm sure u wouldn't want a stiff ride...but then when u need 'sweeping', i'm sure the car tends to roll when u zig zag & would compromise safety.... its a very broad issue here.
my suggestion is all this depends on your way of driving & preferences. what kind of road u usually go, who u always carry with u (don't wanna carry mother in law in a bouncy situation)
best solution is.... be moderate
just sharing....all the best dude