Distributor vacuum advance hitting intake.......

I can tell you this before you get anal about where to turn the slot in the Distributor drive gear; to the engine, it doesn't matter where it is.
The only thing that matters is that whatever tower is above the rotor when #1 cylinder is at TDC compression, gets the #1 wire.
You can spend all day moving that slot 15 times and it will not change this.
Now whether or not you care about having it in the factory location, is up to you.
Furthermore, as already stated, when you drop the D in, immediately push the Vcan towards the firewall. Rotate the crank backwards from #1 TDC compression to about 10/15* BTDC (still on #1 Compression), then advance the D per instructions in post #7. Then mark the Outside of the D as to where the rotor is. Install the cap. Find the mark you made. Whatever tower is closest to your mark, now has to have the #1 wire installed. Then install the rest following the firing order. With the Vcan now as far back as is possible, you will have plenty of room to advance the thing.
As rustycow said;
The factory installation ensures that all the custom-length wires actually reach their intended destinations, and it looks pretty clean when done. Also, if the cap has a factory cast-in "1" at a particular tower, then that will be for cylinder No.1, with the factory installation method. But those are the ONLY reasons to try to install it the factory way..... otherwise, to the engine it just does not matter.