It depends on what your LHS's supplier is. Josh uses Walthers so theres a "middleman."
The engines have to ship from:
China to Shipyard Container Dock in California, where it will sit for a week or two in the hot sun.
Shipyard Container Dock to Atlas by train (TOFC), Atlas inspects them before sending.
Atlas to Walthers, via train if sent ground, Walthers inspects them before sending.
Walthers to Dealer/LHS again via train if sent ground and far away, hopefully your dealer will inspect them before they send them to you, (and the next part applies if the dealer isn't local)
Dealer to you, and hope that it didn't get damaged through the shipping process throughout the entire journey.
Most UPS ground shipments that go long distances are sent by TOFC on trains. Depending on who the carrier is, the train may be delayed, or outlawed, delays in interchange, etc. UPS ground is the most economical way to ship if you have a lot of items to ship.
Some dealers/LHS deal directly with Atlas, which is why they have (somewhat) lower prices and get the items sooner.