I vote 360 cuz it hits more targets more often and most of the time will be happy with cheap gas, and will last waaay longer, not having to run race-gears.
But if you like the rumpidy rump of a big cam, or the feeling of I-did-it-with-a-318, well,just,do it with a 318!
Post 25 is biased towards your goal of hitting high twelves.
In practice,You wouldn't have to run 4.56s ALL the time.They just hit a lot of targets, and help the engine put down more average horsepower during the run, and that is how low-ET is made.
Instead of 4.56s you could run more transmission gears;the important thing is to be running a finaldrive gear that puts your engine thru the traps at an optimum rpm and so that there are no more gears left. This is most important with a small engine running a big cam, cuz the powerband is real small; so you have to keep it on the pipe.
So if 4.56s is the optimum final drive gear, then you can do that with the 4.56s and direct in the trans, OR you could do it with 3.23s and a 1.40 trans gear. The result is still 3.23x 1.4=4.52 close enough. The problem is that the 1.40 gear comes in a 4 speed box and you're only gonna use 3 gears, so you may still trap near 106, but the ET won't be there, cuz the engine wasn't on the pipe long enough or early enough. The best solution for a small engine is more gears.
But there is none for our Mopars, and that is why the 360 (or bigger) is preferred for a dual-purpose machine.
But if there was a 5 speed, with say a 1.30 4th gear, then you could run 3.55s, a very nice street gear. And so 3.55 x 1.30 =4.62 again close enough. This theoretical 5 speed might have a low gear of say 3.57 giving you a starter gear of 3.57 x 3.55=12.7 a really nice race gear. If the other 2 gears were appropriately spaced, you would have a dynomite trans, and a 1:1 5th gear would then make 3.55s hiway doable. So the ideal 5speed for your 318 might look like 3.57-2.32-1.67-1.30-1.00 and the splits are .65-.72-.78-.77. Everybody with a 318 needs something like this. You could run a smaller cam and on a tighter LSA and with less compression, and still hit the targets.
OK here comes my secret, the way I did it;
The Mopar 3.09 overdrive box and a GVOD, used as a splitter.
the ratios are 3.09-2.41-1.67-1.30-1.00-.78od-.54od........splitter gears in red.
the Splits are .78-.69-.78-.77-.78-.73 and of course you now have double overdrive and 7 useable gears. So you can run any rear gear you want. Now you can run those 4.56s with impunity. and you can use5 ratios to hit 106, and still have two ratios to cruise with; one for up to 60 mph and the other will hit 85 at 2600.
The splits are so tight that your 318 will be on the pipe from 20 mph and all the way thru the traps. That means it will be putting down an average horsepower almost equal to it's maximum output. That means it will trap at a higher mph than expected, and that means it will ET better than 12.9.
The converse is, to still trap at 106, you can build your teener with a little less power, and that means, more fun around town.
Is the Mopar/GVOD ideal? no. There are some idiosyncrasies to overcome, chief of which is the very wide splits when not gear-splitting.
To be continued, gotta go to work