Dart swap

Cool, welcome to the site. Magnum as you’re using it refers to a model of vehicle. Magnum as this thread is using it refers to a series of small block mopar engine. You’re all good though, your 79 magnum (car) will have an LA 360 most likely and most of the stuff from that will drop right in to your dart. The oil pan will need to changed. The exhaust will have to be dealt with, and the balance of the 360 is different from the 318 so either you need to use the transmission from the magnum (car) with the 360 or use your transmission with some aftermarket balance stuff. It’s all doable and been done before and is a relatively easy swap. If you have specific questions, shoot. And post up some pictures of what you’re working with and guys can get an idea of what you have.
Edited to add; engine mount brackets between the 318 and 360 are slightly different. Easy to work around with spacers or the 360 mounts are available.