I wrote off my 300zx, 1986 and have a 73 240 automatic, can I just dump the tranny from the 86 300 5 speed into it?

Fml

I miss my 300

Simple answer: No. It has been done but does require some machine work and fabrication. You can use a 5W71C transmission with a 280z-280zx bellhousing to fit the transmission to your L24. It would require some grinding on the bellhousing to clear the front gears on the input and counter shafts and swapping the front counter shaft bearings. Also you'd need to put the bellhousing in a mill and drill out the 5th/reverse shift rod hole to 16mm from 14mm. You'd need to make a trans mount and a longer driveshaft since this trans is 2-3 inches shorter. You'd be better off finding a trans designed for an S30.

No point. The cost/effort is nowhere close to any value of the newer transmission...

Where are you in Canada?