As previously mentioned the whole assembly can't be used directly as the mounting points and the parking brake cables are different, plus the 240 axle assemblies are about 1/2" wider overall.

If you're willing to modify parts, you can make it work, but why not source a good used rear end.

It might be hard to find in your area, but Volvo made over a million 140s and 164s that have a rear end that will bolt right in.

FYI, everything to rebuild a 140 rear end like ring and pinions, carrier, spider gears and bearings are still available new. And there are many companies making locking and limited slip differentials to fit a 140.

Although some of the internal parts can be swapped over, if you have a 1031 or a 1041 rear axle in your 240, the ring and pinion are different and can't be used to replace the ones in a stock 140 rear end.
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Eric
Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
Torrance, CA 90502
hiperformanceautoservice.com or oldvolvosonly.com