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Star Wars OT (1977-1983) In the background, we can see the commercial model kits used for kitbashing.

Cantwell: "Essentially, you take pieces from cannibalized model kits (cars, planes, trains, etc...) as well as shapes from around the office and house. Look closely and you will see pill bottle engines and Easter egg fuel tanks".

These preliminary models then fed into the work of Ralph McQuarrie (here) and Joe Johnston.

This drawing work then feeds into the work of ILM's model makers. So, for A New Hope, there was kitbashing at the very beginning of preproduction (Cantwell), and then again during post-production (ILM).