I've decided to use a C4 alignment, assuming 0.3 ohms in series (to cover a standard good quality series inductor in the crossover) and here's the display of the enclosure properties page after selecting the Vented enclosure.

Relevant things here are the port size (1 in. radius and 5.13 inches in length) and the box volume (0.777 cu ft). We worry about port length because if the port is too long then resonances will creep in. The primary resonance is at a 1/2 wave, which in this case would be about 1 KHz - a frequency where the box will be expected to be near flat. Here I'm not that worried because the final system will be a dual woofer system and the port will be shorter. Also, we can always make the port narrower (at the expense of power handling) and reduce the length.

The next step is to prototype the enclosure and start measuring frequency response and checking the port alignment.