You can try this to eliminate some of the components as contributing to the problem.

Replace the driver's side engine mount with a solid mount, or drill a hole through it and bolt a nut with washers through it and or chain the motor down so it can't lift up any more than 1/2".

This will hold the engine from being able to lift from the torque. I've had issues in the past like this. using a solid mount eliminated the changing geometry of my linkage when the engine moved and pointed me in the direction of the aforementioned missing Marcel spring that cushions the grabbing force of the clutch.

Rigid puck style clutches don't typically have Marcel springs and they tend to chatter unless they are essentially dumped at the starting line or the engine trans is solidly mounted. I still have some of those old solid puck clutches laying around.

It wasn't until the Mcleod Street Twin's came out that I was able to have a clutch live on the street with a high output engine with no chatter.