Tcoat
Brigs were not generally used for transatlantic voyages that late in history.
Brigs & snows have a long history of oceanic travel. The size not being a issue really--Niña was only about 40'/12m overall--ther than it meant that you only had space for non-bulky valuable cargos.
Fine wines, fruit, and similar perishables; firearms, intricate machines; similar "luxury" items were always in demand. Where a demand exists, we humans develop a trade in it.
A brig or snow, being a simplified rig could be worked bay a small crew, 7 or 8, perhaps ten, and only a master and mate aboard. Which also meant only needing to trust a limited number of people around valuable cargo, too.
The stern cabin on the lindberg kit is of a size to have berths for four, so, a Master might rent out a berth or two for a passage.
Another option would be to have a knock-down cabin that could sit upon the cargo hatch to take passengers, too. Such a cabin might have a door with a single deadlight, which a landlugger might describe as a "porthole."
A 12 x 6 hatch would have room for two 6x6 cabins enough for a single bunk with space under it for one's trunk or luggage.