T500 split single

So i bought an ass load of t500 stuff from a fellow who raced one once upon a time.
When i tore into the engine i discovered this.
The crank has been set up so as to fire both pistons simultaneously.
It also looks to have had a few chunks removed from it, possibly to balance it somewhat. I was wondering if anyone has ever heard of this being done, or if someone has any insightful info about this setup.

Sears sold an allstate (?) Motorcycle using a "twingle" engine, but iirc it used a shared combustion chamber head.

What you have there definitely looks neat, but I'm unsure of what you'd gain from that configuration. Interesting piece though for sure.

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I guess the theory is to have the power delivery and engine characteristics of a big single, but with better port arrangements?

Any idea how the two halves of the crank are joined? Is there a keyway in there somewhere?

I have several spares now, but if this one was indeed balanced it would be ideal to set it back to 180 firing.