If your Ranchero is a street car, I think what your really looking for are changes that will make more torque. That being said Techinspector's comment about a 351W swap is the way to go There really is no replacement for displacement and the bore and stroke increase is an night and day difference.

The following suggestions apply equally to all 289/302/351W.

The area that needs improved the most on SBFs is the exhaust, The stock exhaust manifolds and single exhaust are marginal with even a a stock cam and 2BBL carb. 1 1/2-1 5/8" primary tube size headers are about the best thing you can do, but if you don't want the hassels of headers, scrounge the wrecking yards for a better set of manifolds that will fit your truck (some of the 70-80's 351 powered ford trucks had decent sized manifolds), and port match the exhaust ports. 2 1/2" dual exhaust behind the headers/manifolds is nice, but 2 1/4" is really sufficent and often easier to get over the axle.

The SBFs also like more cam than the factory installed. On a street car unless your really planning on spinning your engine into a high RPM range (above 5500) keep the lift under .490 and the duration below .290. Look for a cam with a little more lift and duration on the exhaust side than on the intake. You also need to keep in mind that a cam that is ideal for a 351 will likely be a little too much for a 289/302.

A good dual plane intake with realatively small runners and a 4 bbl in the 600-650 range just about covers the bolt on.

If your budget allows a little better set of heads will also help (early 351W or aftermarket) but keep an eye on compression as there a ton of different chamber sizes out there that can either cause too much or too little compression. Don't over kill it by going to the 2.02 or bigger heads as these will actually hurt performance on the street. Keep valve size to 1.90/1.60 max especially on a 289/302.