they can be good castings if you are on a budget. The fact that someone went to the trouble to put the larger valves in and decent springs is a good sign, b/c that is typically what can cost some dough. They should flow about 180 cfm on the intake even w/o porting, which is definately an improvement over 5.0 heads. Minor port work and 200 cfm is right around the corner. The other thing to check is the combustion chamber volume. Most 351w heads should be around 66cc's i believe in stock configuration, and if you mill that down to 60cc's or so, you should pick up some hp (assuming this hasn't already been done). Of course, if you want major HP, nothing can beat the new aftermarket castings, and if you go that route, you have some heads there that should be worth a couple hundred bucks to someone.