ENGINE BUILDER.....
A person who can spec out components for a predetermined amount of power or a predetermined use and take each of those components and perform the duties to that said component until it is ready for final assembly....then assemble the said components into a running engine....and tune it.
ENGINE ASSEMBLER....
A person who may be able to spec out components for a predetermined build but has them prepped at a different location by someone other then themselves to be ASSEMBLED by them into a running engine.
BIG GIANT DIFFERENCE....