It depends on what you want to do. If you plan to rebuild the motor, I would look for a nice low price one to start with.
If you plan a performance, but close to stock build, a roller block is a good start. Note: even the roller blocks are not full roller; they still have the conventional rocker arms on it. Full roller is a roller cam AND roller rockers. The only time that rolled out of the factory is the ’93 cobra. Those are a little pricey considering you can just bolt on a set yourself.
If you plan to just get an engine and drop it in as is, you have to consider condition. The ’69-’70 engine was the best there was, but they are 35 years old now. I would never pick up a stock engine that old and just drop it in.
For the most part anything from the 70’s and newer will all be about the same.
The latest engines are the mid 90’s engines. These engines are available in 2 flavors. The light truck, and the heavy duty. Before you go thinking “lets go get the heavy duty” think of this: The heavy duty was meant to run at full throttle all the time. Sounds good right? Wrong! The compression was dropped from 8.8 to 8.3 to prevent problems in the engine. This takes out a big chunk of power. The rest of the engine is the same. The light duty (F150/big Bronco) engine will out run the heavy duty (F250 and up) engines. If you were to swap the engine into a boat, I would recommend the HD engine because they were built to run hours at full throttle. Sacrifice a little power for longevity. Consider how long you drive at full throttle? Witch engine better suits the needs of a bronco? The ZF (if I remember right) is typically found on the HD trucks, the ones with low compression engines.
As for a rebuilt engine, all bets are off. Pistons and cams can be changed to almost anything and it could still fall into the category of “stock rebuild”. Flat tops replacing dished and vise versa. Factory cams came in dozens of grinds, most of them bad for performance as they were each trying to squeak the engine through tighter emissions. Anything that has gone through a rebuild house I would consider suspect.
It basically comes down to getting a good engine (weather you build it or just fine one used in good condition). Don’t take anybody’s word about it. Look for cars and trucks sitting in the junkyard because of accidents. A cherry car sitting there is probably there because the engine died.
And for fuel injection, please do a search. There is enough stuff on this board to keep you busy all weekend.
