In shiparch.ini you need to add a bunch of stuff that's missing like camera settings, weapon hardpoints (CSV has 2 + 1 turret), straffe force, nanobot and shield batt limits and a shield. You can pretty much just look at one of the pilotable ships and see what you need to add, as far as the hardpoints go you can look at the cmp file with the UTF editor or look at loadouts.ini to see what the NPC pilots get.
Then you need to add a hull and package in goods.ini, if you're not concerned with infocards you can just use the IDs from any other ship.
For completeness you'll also want to make your own engine and power for it, if you use the current CSV engine you wont have all the sounds or a trail behind it when you're flying it. Engines are in engine_equip.ini and power systems are in misc_equip.ini.
Then in market_ships.ini, you'll need to find rochester, I think that's Li01_12_base but double check that, it's the only base in Li01 selling one of the Pirate ships (pi_??_package) I can't remeber which one it sells normally, i think it's the lf (Bloodhound) but dont' quote me on that
There are some tutorials in the tutorial forum the cover adding other ships to the game, you can just follow them but use the CSV instead and you should be able to figure it out from there.