Swapping the entire Tesla rear subframe into a 240 isn't happening easily.
Even the Model 3 is a LOT wider than the 240.
There has been a company that built a cradle that fits a Tesla drive unit and bolts into a Jaguar XJ6…using Jaguar style suspension.
This wouldn't be too hard to fit in the 240.
Alternatively, you could build a cradle to hold the drive unit and fabricate a DeDion axle running the original 240 suspension.
This would be MUCH easier if you can switch the motor to run in reverse, as it would sit nicely in there and clear the factory Panhard bar…but otherwise you could go the other way and mount the axle in front of the drive unit with a Watts Link in front of the axle. Not technically hard to do, but will need engineering.
If you have a Model 3, the battery modules are either bonded in the car, or are nearly 2 meters long…even if you repackaged them you'll have them hanging lower than the sill.
Model S or X modules are easy to repackage. They are about 900mm long, 300 wide, and about 80 thick.
