You mat want to go with the mini baja motor. If you try a 300 size, or larger, you'll have to re-drill the motor plate...I made my own with aluminum stock and a dremel. I run an Orion Bigblock with 7 cells, and it's plenty for me. If you want more in a brushed motor, you could also use the Sportwerks E370 (same size can).
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If it don't fit, force it...If it breaks, it needed replacing anyway.
The Insane looks like it uses front and rear bearins and it seems to have replaceable brushes, while the Frenzy uses front and rear bushings and its what you call a throw-away motor.