It represents a X-35A, the version with a SVTOL system behind the cockpit and rotatible jetpipe.

The real X-35A flew first as a prototype, now it is being converted to the X-35B.
The X-35C is the Navy version with enlarged wing tips, separate aileron and larger horizontal stabilizer. It also has an arrestor hook.

The model depicted here, as provided by Italeri, is the X-35A.

 kit's parts

1- The wing fairing at the cockpit sides should have a little less width, remove 1 mm.
This will also give the wing-fuselage junction the needed small kink at the wing Leading edge at the root. Remove some plastic, fill and sand smooth. 

  some suggested corrections outlined in blue, 
 

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The two lower fuselage "belly" bulges on part 11 at the main undercarriage sides should be removed; sand these flat.
 
 
 

 note the belly fairings, to be sanded flat

two fuselages of two kits: right with cut- out parts to correct it further. Right part not sanded flat yet.....

Main undercarriage should be moved approx 5 mm more forward, and reduce the length of the main bay. In fact, the bay opening should  extend somewhat more inboard on the flat lower fuselage (not yet seen at the pics...)

The legs should also fit into the fuselage and not into the wing.
 
 

The bulges (15/16) at the intake should run a little smoother, so use some putty here. Sand first before added the intakes (31/32). 

Glue main parts together, fill and sand smooth. 

Note that the main u.c. bay opening above is not yet correct, this is shown below....

The main u.c. bay opening is extended to the flat underside.
 

The vertical tailfins are OK, but they should be fitted 1 mm more outboard. Cut out the outboard edge of the locating holes and glue the fins in place later.

 

The tail area: note extended slots for the vertical tailfins to move them more outboard.

When you built this kit:
- The cockpit will benefit from adding some more detail.
- The small intake doors on top, on the left side and APU are missing before the wing LE. 
- Add some antenna’s and the nose pitot if desired.
- Add a fairing at side of the lower left main undercarriage door. Not yet seen on the pics...
- You can also add two thin brakes at the lower fuselage at the rear (not provided and not yet seen at the pics here...).

A small set of decals is provided for a X-35A prototype but they are not correct .... 
 

If you want to make a US Navy SVTOL X-35C adjust the following:
- make the larger wingtips with separate aileron. Extending the tip will do the job.
- add the lower aileron fairings
- add an arrestor hook and fairing
- fill the door aft of the top intake on the top of the fuselage and add refuelling panel.
- extend the horizontal stabilizers slightly and change the hinge line of the stabilizers aft of the vertical fins.

Note the correction at the  wing fuselage junction and single piece door of card. The engine covers are also in position. The wing flap and slat gap are left open. The APU exhaust is added in the forward fuselage and the main wheel struts added, needing only cut-off of their locating pins. 
 

A view of the model prior to final clean up and ready then to get its first grey base coat. Pitot tube added from a needle and exhaustpipe (APU?) on the right intake

The main intakes are added as is the nose undercarriage. It has newly made doors from card. Also note the closed and filled auxiliary doors aft of the n.u.c. bay.

cockpit area with some added sprue details. Some sanding work to be done still...