This is a torsion bar arm for a sprint car. It goes on the front end of the torsion bar and rides on the front axle giving it support. The first URL shows one very similar to yours and explains how they work. MCI is just one maker of these. The second URL shows one that's very close in design to yours made by M&W and sold by Speedway Motors. These come in various shapes and sizes. Some are straight, some curved or off-set, most have the same spline. Unfortunately, I could not find an on-line picture of the MCI Chassis arm.

This is a torsion bar arm for a sprint car. It goes on the front end of the torsion bar and rides on the front axle giving it support. The first URL shows one very similar to yours and explains how they work. MCI is just one maker of these. The second URL shows one that's very close in design to yours made by M&W and sold by Speedway Motors. These come in various shapes and sizes. Some are straight, some curved or off-set, most have the same spline. Unfortunately, I could not find an on-line picture of the MCI Chassis arm.

References:

http://www.world-sprintcar-guide.com/sprint-car-torsion-bars.html

https://www.speedwaymotors.com/M-W-TA-17A-Angled-Torsion-Arm,29224.html