318, 340, or 360?

The early As don't really NEED a 360, to be even moderately nasty.
But like 273 said, the 360 will allow you to do more with less.
You don't NEED a big cam, so also don't need a high stall . Because the 360 can make so much low-rpm torque, You get to run a sane 3.23 gear, and a 904.You don't NEED hi-flo heads, or a Big intake or a big carb, etc
Now you can put all those things into your combo, but you will then have to spend a bazillion bucks on the chassis to make it hook. .
I'm with 273
If you have no engine to start with you can't go wrong with mild Magnum
And an A-904 with a 2.45 low. This will get you about 6150@60mph in first,3630 in second and 2500 in direct. Perfect for 3 targets; Zero to 60,kickdown to pass, and a real nice cruiser gear.
Additionally you get 32mph = 1950 in second,3300 at kickdown.

If that interests you; then just build the 360 Magnum to pull hard at 3300 up, to pull to about 5800, and to make mileage at 2500. Easy-peasy. A fast rateof lift roller of about 262 advertised will git it done, with perhaps [email protected]. With one more gear you could pull some impressive mpgs outtof that combo, and be driving cross-country with not enough fuel stops to satisfy your aching bladder.
;
But if you're a stickman, and not interested in cruise economy, well then;just slam some 3.55s in there, with a 3.09 low trans.. These will get you a fabulous starter gear of 10.97 and 65=5500 at the top of second, with a cruise rpm of 65=2870
At 32 mph, the rpms will be 4360-2690-1976-1411; not exactly stealthy, unless you can backshift from third to first; Ka Blaam!!