360 magnum swap in 68 barracuda
I thinking about just using the V belt system with A/C compressor and power steering. Also carburetored
Relatively easy, then. Just swap the timing cover and water pump over from your 318, and maybe the distributor. The early TC and water pump allows you to keep your current radiator and accessory drives. Then the rest should bolt up. You will have to re mark TDC on your harmonic balancer for the old timing cover. As 66fyssh said, you MAY have to do a clearance grind or two, especially by the starter. Some headers have also been known to have interference with the mid-block Magnum mount bosses- a bit more grinding there.
Things to start looking for:
An LA360 pass car oil pan and pickup (if the Magnum is not already equipped with a center-sump pan). Your 318 pan will not fit the Magnum.
A Magnum 4 barrel intake (again, if your Magnum crate engine does not already have one). LA manifolds are not the same. Speedmaster in the past has run a Black Friday sale with something like 40% off, so that's coming up...
A 5.9 Magnum flexplate. It has the balance weights to allow you to run your '68 torque convertor.
A set of headers or later ('73+) A body manifolds, preferably 340/360 units. Earlier manifolds ('67-'72) MAY have some slight interference issues with the Magnum heads, and Magnum exhaust manifolds will not fit A bodies with power steering. Thus the headers or later manifolds.
Save all the bits and pieces from your 318; motor mounts, linkages, etc. they can all be made to work on the Magnum. The motor mount mods are well documented on this site. The throttle linkage mod is here:
Throttle Bracket for Magnums