I think there's three options possible here.

1st option is to remove the heads and get them re-drilled for the "LA" engine bolt pattern. This has been talked about on this board several times lately. Then you could continue to run your existing TBI intake and injectors.

2nd option is to find a 92 or 93 d150 that has the 318 magnum and getting the underhood wiring harness for that vehicle. I can't guarantee that the wiring is 100% the same but it would be by far the closest. You'd also need the fuel pump and probably fuel lines from this trucks gas tank. MPI and TBI have different requirements.

3rd option is to buy one of Mopar's carburated intake manifolds for the magnum engine and then have an adapter plate made for the TBI.