For what it is worth I have heard of very light 318's being set on a /6 set of mounts and suspension with some tinkering. With the 360 you would absolutly need a new K and suspension parts.
I do not understand this part of the post. There both V-8's with a weight difference of very little between 2 and 4 bbl engines.
On a look of HP between the 2, the stock /6 suspension is equally at a disadvantage. The torsion bars could be a hair thicker for the car/engine combo. But it's not a must do. IMO, it would be nice to swap out for the next step up in thickness for better road control. The /6 bars are good for weight transfer. Next up is the stock bars and for a firmer ride, theres the big block bars. A good set of modern shocks and a set of thick sway bars round it out well.
On the 318 vs. 360 cid, the 360 has greater torque making abiltys while maintaning better street manors and drivabilty. 40 HP with some preped heads and a mild cam is easy. You would not need a cam of more than 230 @ .050 duration.
Headers are the real trick and the ones that fit right are not cheap.
I used to have a 360, stock with dual exhaust of the manifolds and a small Carter 4bbl (625) fired by a MSD getting 20 mpg's in a heavy '79 Dodge Magnum with 235/60/15's tires and a 2.76 geared rear.
