Paul,
The order that you show is correct for your 390. On my FE the #1 on ther distributor is almost directly in the rear of the cap as you look at it from the front. This can be located in a different position as long as you make sure that you have the firing order correct. I ran it for years with the #1 Distributor Cap location on the right side, before I pulled the distributor and corrected it back to the way it came.
TDC is when you have the #1 piston at the top of it's travel. I use a simple way to determing this. Take the plugs out, turn the motor over with a small wire gauge in the plug hole resting on top of the piston. When it starts back down you have passed TDC. Once you have that set, then put your distributor in with the rotor pointing to the terminal that will go to #1 piston and then make sure to wire all the rest in the correct firing order. The older caps had the #1 marked on them but they don't seem to do that any more.
Ron
