I found this addtional information about the Tamiya F104X1.
Tamiya F104X1 F1 Chassis
This new kit is based on the F104 chassis. Its designated the F104X1 chassis and its a limited edition release. It was created to further improve traction and cornering performance. It features newly designed parts that include a roll damper as seen in many 1/10 and 1/12 scale pan cars and a new X-shaped upper deck. This limited edition kit also sports special-colored aluminum parts.
NEW Specifications and Features
The below parts are new to the F104X1 chassis kit (Note: some items are only new in terms of color)
X-Shaped FRP upper deck (new part)
Aluminum damper mount (Titanium color) (new part)
Rear axle shaft counter weight fitted with ball bearings (black color)
F104 carbon reinforced gear case (new part)
Aluminum Roll damper (Black color) (new part)
Item 54129 TB-03D Aluminum Motor Mount (new color)
Item 54158 F104 Aluminum Diff Housing Set (new color)
Item 54159 Aluminum Horn for Hi-Torque Servo Saver (F104) (new color)
Item 54202 F104 Aluminum Upper Suspension Mount (new color)
Left Rear Wheel Hub (new color)
Standard Specifications and features
Link-type front suspension
Front kingpin coil spring independent suspension
Direct drive solid rear axle transmission
Accommodates Tamiya foam or rubber tires
Fits F104 specific F1 body shells (sold separately)
Adjustable front camber
Adjustable front and rear ride height
Other Included Option Parts
The below option parts are already available as option parts for the standard F104 chassis and come standard on this limited edition release.
Item 53599 Fluorine Coated 5mm Aluminum Ball Nut
Item 53901 TRF Special Damper (F103GT) (Black)
Item 54154 F103 Carbon Reinforced Front Upright
Item 54160 F104 Titanium Coated King Pin
Item 54161 F104 Low Friction Suspension Ball Set
Item 54222 F104 High-Traction T-Bar
Touring Car Short Spring (Black)
Low Friction 5mm Adjuster
3x35mm Aluminum Turnbuckle Shafts (Black)
4mm Aluminum Lock Nuts (Black)
4mm Aluminum Flanged Lock Nuts (Black)
New specification highlights and details
Roll Damper & Upper Deck
Pitch movement is controlled by a single TRF Damper and roll movement is controlled independently by a new Roll Damper. The Roll Damper connects to the FRP Upper Deck, which features a new X-shape for better roll characteristics, resulting in improved traction.
The rear shaft counterweight is installed between the gear case and the left rear wheel to optimize balance and improve rear wheel traction. This freewheel counterweight is equipped with a ball bearing and does not affect the cars acceleration.
New durable gear case
Compared to the standard fiberglass-reinforced parts, this Carbon Reinforced Gear case features superior strength and enhances the effect of the Roll Damper.