If you are asking what a SOHC engine is, it is a standard modular motor that uses two cams (one per head) hence how they get single over head cam (SOHC). They eliminate the need for pushrods and lifters, by using a gear to drive the cam and open the valves. They switched to these designs to better fuel efficiency, and also has other benefits like a higher rpm range compared to an OHV engine. Neither is "better" they use both designs in modern engines. Hope this helps.
the 4.0 V6 is chain driven- and weird... there is a chain that drives a dummy cam, a chain on front of the motor from the dummy cam to the passenger head camshaft, the rear of the dummy cam drives another chain to the drivers side head...servicing that requires engine removal- guess the thinking was to keep the decades old productiion machinery from the cam-in-block days around to produce a overhead cam design...also believe this approach only required one head casting be designed.
aside from being a bit heavy as its all iron, and its weird jackshaft drive, its a durable motor, makes decent power and due to its quite large size for a six, it sounds pretty decent too
never heard of any head gasket issues on these, unlike many aluminum sixes ford has built over the years.
My wife has ran her 07 pony down the track quite a few times, totally stock, put in drive and floor it- but she had fun, ran mid 16s at 90mph.
we took ours out west this summer (5800 miles in two cars with the 4 kids) and she consistently only beat my stickshift 06 GT by only 1-2 mpg, so I dont think its the most economical V6 out there, but it was made to be a good match for a 'fun' car, not a econobox
enjoy it- as others mentioned, suggest picking up a spare thermostat housing, its on my list of things to do, they are about the only issue these 4.0s had- but a LOT of them are cracking. Love that vista Blue- we have 06-07-and 09 all in that color here