If the engine is out of the car, does it affect this project at all? how best to do this?

I want to replace the UCA's and the bushings on the firewall for the sway bar.

It is best to only replace the sway bar bushings now? Do you do that with the tires on the ground or raised off the ground?

It sounds like you need the weight of the engine to replace the UCA's to position it properly before torqueing. Is that correct? If so, I should only replace the firewall sway bar bushings now and wait to do the ones at the UCA when I replace it?

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.