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Build table:
Ensure it's both level and flat.
Set build table height so that you can reach in and access the center without climbing up on it.
Compromise this with the table height being such that when seated, it's at a convenient height.
Also consider how to access the large storage space below it. For example, can the drivetrain be rolled under the table.
Think about how an engine hoist can be rolled up to the table to place the drivetrain, will the legs of the hoist and table hit?
Extend the table top a bit over the edge of the table frame. This comes in very handy for bending metal over, or clamping objects to.

Create and place jigs that represent the inboard ends of the A-arms, then build the chassis out to meet them.

Place major parts - engine, transmission, gas tank, seats, pedals - in position on the build table Before starting the build.

For the drivetrain, fabricate a stand that holds the drivetrain at the expected height and orientation above above ground (noting that the distance between the pan and table will be very different than from pan to ground). Do not connect the stand to the engine or tranny mounting points. Same as with the suspension jigs, this allows building the chassis out to the drivetrain.

Motto: Use the actual parts to tell you where the chassis needs to go.

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Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/