The old trucks had a braided (woven) wire cable from the negative battery post to the nearest bolt on the transmission. You always want to make electrical connections from point A to point B by the shortest distance possible.
An engine-to-frame connection connection can be made just about anywhere, but pick a heafty-sized bolt on the lower part of the engine to a nearby equal-sized bolt on the frame. Check the Tech Tips for a location. One good spot is from the mounting bolt that attaches the starter motor to the engine, then to the frame.
One good reason to attach the negative braided (woven) cable to the transmission is that the metal between the starter motor and the transmission is a fairly short distance and all the metal involved is big stuff--good for a low-resistance path from the starter motor back to the battery. Be sure to use a BIG positive cable from the positive battery terminal to the starter motor stud, and keep it the proper length. Electricity hates to wander through a wire that is too long in search of the next terminal. The braided cable from the transmission bolt to the negative battery terminal need be only about 8 or nine inches long at most. You can buy one of these from your local auto parts store that really deals in good service.
Provide the shortest possible distance from the positive battery terminal to the starter motor then from the transmission back to the negative battery terminal.
The engine-to-frame connection connects up all the peripheral stuff that uses electricity, such as headlights, brake lights, clearance lights, dash lights, heater motor, etc. In fact, for than one engine or truck bed/cab negative connection to the frame will get those little electrons heading the right direction and save you lots of voltage drop on the way.
Resistance in an electrical circuit increases with the number of connections and the total distance the EMF has to push the electrons from the positive poswer source to the final negative ground.
Oh, t'heck with all that theorethical mumbo-jumbo! Just get your truck running and drive it!
