318 Magnum first fire...timing?

In the video, it sounds like it's trying to start, so then the D is probably installed at least close to correct. When the D is out by 180*, the engine usually just winds up and sounds like the ignition is dead, with no fires whatsoever; because every plug is firing on the end of the exhaust stroke. I suppose it would be possible to have an afterfire in the exhaust with a big enough cam, but it has never happened to me.

It sounds to me, like the AFR is just not close enough. A cold engine wants a lotta fuel. Not to get the gas exactly, but to get the small droplet size that will support combustion; and this is also why the gas in the floatbowls needs to be fresh, because the fresh fuel contains the VOCs that aid in starting. Once the VOCs are gone, your gas is stale and becomes hard to light-off.
The big drops just puddle in the intake, or stick to the runner walls, like rain sticks to your windshield at speed. That fuel will get sucked into the chambers after the engine starts, and after the intake warms up a lil. Some of those gas molecules need to get up to close to 400* before they boil, whereas the lightest VOCs flash in the 90s..

At this point, your engine may be flooded.
When that happens, it often washes all the oil off the cylinder walls and you end up with poor cranking pressure.
So what I do is, on first start I mix the bowl fuel with 2-cycle fuel at about 5%.
But at this point, just to rule out flooded, I would pull the plugs, disable the Coil, and pump the gas out of the cylinders, and then put a squirt of oil in each hole, roll the engine over one turn, and inject another squirt, then walk away for 30 minutes.
When you get back, that oil will have, by capillary and creep, found it's way to the rings or cylinder walls etc. and you can pump the rest out. Yes it will make a mess, so prepare your engine bay.
Ok so pump it out with just a few revolutions, and re-install your plugs.
Then, assuming a flat-tappet cam;
Prove your timing is set to at least 15* advance.
Install the V-can hose.
Engage the choke in relation to your ambient temperature,
make sure the PCV system is installed correctly,
clamp the booster hose if you don't know it's history, and
start over.
As soon as it fires; get it up to 2200,and look for fuel leaks. Finding none; pull in all the timing she'll take, without regards to the actual numbers, until more timing does not produce more rpm. Then reset the Rs to, in the range of 2200 to 2500, and then take out a tiny bit of timing. Finally, let her alone for 20 minutes, watching for leaks.
By giving the engine all the timing she wants at 2200/2500, the required throttle opening will be less, so she will be burning less gas, making less heat, and keeping that heat in the top of the cylinder, thus helping to prevent overheating.
After the break-in, you will have to work out your timing ; do not leave the timing all pulled-in like I described. But before you change it, check it, because whatever it is, it will be close to what your engine will want, to cruise the hiway with, for best fuel-economy.