Jim,
I got the oil plan from one of the parts vendors. Probably CJ pony parts. They all sell the same stuff. It's and import knock off, but it fits fine. That reminds me of another thing though. Be sure to use the oil pan shim rails from the 5.0 as the oil pan bolts for the 5.0 are slightly longer than an old 289/302. If you don't shim it, it will leak because the bolts hit bottom before they completely tighten.
I used the front cover from my original engine. They are also available at Mustang parts vendors. I used the old V-belt system. If you go with serpentine and the 5.0 pulleys, use the 5.0 water pump as it is a reverse rotation.
And another thing I forgot, if you go with the 289/302 flex plate or flywheel and rebalance it, you must get a new harmonic damper for the front to be compatible with the engine balance. All of this stuff is readily available.
Dale