First up, does the 340 have the pistons that go above the blocks deck?
If so, make sure those are the right Edelbrock heads.
Secondly, the question is combo dependent. IF your simply just swapping the heads out, the Edelbrock heads will perform like and feel like a well done bowl porting on iron heads.
How much speed this will net you at the track is also a combo dependent issue.
Worth the money is also a personal issue. IMO, a new set of Edelbrock heads are *** amount. How well can your J heads be ported to for the like amount?
Everyone points to the weight savings of the aluminum. It's not a big deal. No matter what they say or how they say it. While a drag car will like the weight savings, there also doing it all over the car. So, a 25 lbs. drop is good. On a everyday street ride, you'll not know the difference.
IF you can have your J heads ported to match or come really close either better or not, than the Edelbrock head, is 25 pounds worth it to have or is it a must have?
