Well there really isn't a easy way, but the simplest way.

If you are starting a automatic truck you can start by mounting the stock trans mount to a 904. That will bolt up to the stock crossmember, speedo, driveshaft and shift linkage. That will set your 318 water pump snout even with the front radiator support, which you will have to cut out to get the engine in then fab up something to replace it. (Setting the engine this way is going to have over half the the engine in front of the tires centerline, very nose heavy)

After that you will need to cut out the motor mount towers and Fab up new ones and weld them in.

Center dump exhaust manifolds are going to be a must. There is no way around the starter and steering box for rear dump.

Custom oil pan and oil pick up tube and/or front crossmember.

Find the biggest radiator that will fit up against the grille and fab up a mount.

If your keeping the hood you will need hood pins because the hood latch would have been removed with the radiator support.

Unfortunately I don't think anyone has ever done this the same way twice. It's really just a custom thing you have to do by trial and error.
But hopefully that kind of gives the idea of the easiest way that I would know of doing. By far not the best way.