Advice needed...

273 has a good idea;
if you have room cylinder-pressure wise,put the cam that is currently in the 360 into the 340Dart, and a lil smaller cam in the 360 TRUCK.
See at 9.5 Scr, the 360 is currently low on cylinder pressure. You don't notice it because A) it's a 360, and B) you have a lightweight-A, and C)you have a clutch.But with the next smaller cam, that pick-up will really jump.
But if you put that same 268AH cam into the 340 at the same 9.5Scr, then you are gonna lose a bunch of torque at lower rpms, and if you install the 284, it will be even worse, and now you have the unhappy consequence of having to drive deeper into the carb all the time, and you can't seem to keep the fuel-tank full.Your first thought will be to ditch the 3.55s and the next one will be headers, so there goes about a grand.
So, Ima thinkin, to get around that, get you a Solid lifter cam of [email protected] and fast ramps to keep the pressure up at low rpm, and of course lotsa pressure. Without headers and a free-flowing exhaust, there's not much point in running a big cam, because the overlap period is neutered.You end up with a wicked sounding idle, a pig on gas, a soft bottomend and a choked top with a missing spike from the stalled overlap.
Remember how much power 340s picked up, back in the 70's with nothing more than headers and a re-tune? And that was with just 44* of overlap. A 284/292/108 has 72* of those ........... almost none of which are gonna do anything except make a wicked sounding idle, waste lotsa fuel,and make the bottomend soft ........until the headers go on, with the matching exhaust.Then the spike will be there. Without cylinder pressure, the bottom will still be soft. And you can't change the fact that it will be hard on gas; the extraction period is NOT street friendly at just 102* when installed at 104 degrees..