ZF trans in a 240 TD would be neat, the ZF trans and D24T are a great match for each other.
I think you will find that trying to put the engine into the 240 at the 740 angle would cause some interference with the heater hose connections at the firewall, and of course it would create quite a bit of work making new solutions in many other areas where you could otherwise use stock D24 pieces if you kept the D24 angle (e.g. D24 radiator hoses that might no longer fit, radiator fan would probably no longer be centered in the shroud so would need custom work there, A/C and steering hoses, etc). That is in addition to the crossmember and engine mounting surgery you mentioned and the possibility that that might make it harder to pass a safety inspection.
Here could be one alternative: If you got creative with the transmission mounting and shift linkage, you might not need to use the 740 mounting angle to keep the ZF trans. You might be able to retain the D24 mounting angle and mount the ZF transmission at an angle also instead of the square orientation it has in a 700 series. I don't think the transmission would mind being installed with a few degree clocking angle, which is all it would be, since lateral forces from cornering are frequently greater than the angle difference would cause anyway. You would need to figure out the right level to fill the trans pan to mimic how it works when mounted at a flat angle but that shouldn't be hard, you could make some custom marks on the dipstick once you have it dialed in.
I think in some of the ZF 4HP22 applications the trans is even mounted at an angle from the factory (Pinzgauer if memory serves?) and uses a canted-bottom sump to compensate for the angle, and the filter/pickup screen might be different for those too. If that is true it could provide some more options.
The 240 D24 M46 or M47 manual gearbox is always an option for a bolt in setup if you don't find a way to use the ZF. But you'd have a unique and nice setup if you manage to get the automatic to work in there. Let us know how it goes.
