[davepl]

Number one is wherever you decide to hook up the #1 plug wire. Generally it's a case of whatever make the most sense for routing the plug wires and leaving yourself enough rotational room so that you can advance and retard the timing without the distributor running into something when you rotate it.

Otherwise, however, there's no special number 1 terminal on a old setup like this. The order matters, and the alignment of the rotor at TDC vs. whatever terminal you picked matters, but you could do them however you'd like.

FWIW, the assembly manual DOES show a preferred order (not for HEI, though, if that matters).

Firing order determines which plug wire comes next, and which after that, and so on.