Basically what Dave S said is true - there are some significant internal differences that might concern you if you mix and match rotating parts, i.e. the balance is 50 in oz, beginning in '85 rather then the older 28, main seals are different, flex plate/torque convertor bolting is different. The front timing cover and pulleys are different, the newer being serpentine, reverse rotation drive which will make the engine a couple of inches shorter, but the older stuff can be interchanged. The oil pan on the newer engines is usually a rear sump - but again, with the right pump/pickup, not a problem.

Motor mounts are the same thru all years.

There is a Ford Parts Interchange soft bound book by George Reid (as well as many others) that covers most of this as well