Drilling a straight hole under the car like that is difficult.

If you can get the hole to be the same size as the bolt needed to attach the shock (what is it M10?) you can use a longer bolt and a stiff nut on the other side of the nadgered threaded portion of the trailing arm. It is tricky to do this but I have managed to hold a nut in place with bent needle nose pliers stuffed through the coils of the spring.

The best option however is to remove the trailing arm and grind off the square threaded block and weld on a new piece.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!