Seems like 60's Ranchero's are getting scarce nowdays...nice score!!
If it was originally a 289 powered vehicle, the rear will be an 8" inch. Dont fear the 8" inch, a 5.0/302 will not break it.
You say it has manual brakes, are they front drum brakes??...if so, its an easy swap to put factory disc brakes on it.

To put the 5.0 in it, you will need to change the oil pan and pick up tube to the early front sump style...easy to find.
You may also have to change it to an early style water pump because the hose inlet is on the opposite side than the late model engines.

As far as mounting it in the chassis, it is a direct bolt in with the stock mounts.