My 2 cents.
I weighed the aluminum block option. First it is a nice peice. Probably does
oil a little better than the original Ford/Edsel. It is expensive though.
Cool better? Yeah probably. Still going to run approximately the same temps though. In fact two of my friend's CSX Cobras both with aluminum blocks and heads runs hotter than my original FE. Don't know why but they do. Go figure.
Power? Iron heads will make more power than aluminum so I was told.
The difference in weight between the blocks is no where near 200lbs. Its more like 50lbs. This is what I was told.
Durability? About the same unless your really pushing it. Then the nod would go to the seasoned iron block.
Originality? Iron block all the way. If your block is in good condition and is no more than .15 over your fine. Defects. Thats what pressure testing and sonic testing are for. The new aluminum block is a center oiler. Its not even an SO. Many of new aluminum block motors are taken to 454 via stroking also.
Strength?. No way your going to tell me that an aluminum block has more structural integrity than a solid condition seasoned SO block with cross bolted mains. Especailly a REAL full race NASCAR SO block with high nickel content, forged crank with extra wide journals and NASCAR rods. Sorry sell that stuff elsewhere.
Value. Depends what your after. If you are going for pure originality and aesthetics there is no choice. Both engines, iron or aluminum if done right will run between $20K and $30K.
While there are only a limited number of originals and the rest replicas (with the CSX being the only REAL Cobra replicating the original-Sorry had to get that in) of the original if you want the same heart that beat in the original Cobra and all the sensations and intangible satisfaction of knowing that you have the same power plant that made the Cobra a legend to begin with then again there is only one way. FE. Period. End of game.
And more specifically, if you have a CSX, new or old you can justify either approach. The new CSX is correct with either engine because it is a Cobra, not merely a replica of one (sorry) regardless of which way you go. There is no right or wrong. Old or new. I chose the original '65 427. I wanted my car to clone its forefathers in every respect. I wanted it to be the same car separated by 40 years in gestation.
There is an intangible excitment and thrill knowing you are feeling the same performance and power dished out by your Cobra's anestors 40 years ago. Its a rush and a trip back in a time machine every time I get behind the wheel. Just put the Stones or Steppen Wolfe in the CD player and your back in 1965. The ultimate trip back to the future.