Well, I just finished the same swap.
I dropped a '94 Magnum 360 into my '85 Ramcharger. Complete minus the EFI setup, but all accessories! (Its beautiful!)
The EFI would be to time consuming to make work on the older vehicles. I swapped it for a MP dual plane intake manifold and carb.
As far as if it will fit, the answer is you have to do a bit of cutting.
The power steering pump hits the driver side frame rail.
Other things to change:
FLEXPLATE: Forget the stock one. Won't fit anything but a late model lockup converter; go with the B&M SFI flexplate for the late model 360 magnums. Cut the weights off your torque converter if you plan to reuse the old one, or get a unweighted converter if you change it.
AC: If you can rob the hoses of the donor vehicle you can problem get new compressor to work.
EXHAUST: The Magnum exhaust manifold are much better than the older LA manifolds, but the exhaust exits from the rear instead of the middle. Magnum and LA headers are pretty much the same of you want headers.
IGNITION: If you go with a intake and carb, you will need a older distributor with vacuum advance.
I have pictures of the install. Email me if you are interested.