53 kind of makes sense if you're taking in account that Thunder Teams are around 52mm? But realistic I'm not sure how much change that is
Thunders with forged plates are 52.5mm, the team editions have a cast baseplate, and are 53.5mm, the same height as forged Indys.
Having switched from the forged baseplate to the cast baseplate, a mm can feel like a pretty big difference. I'm pretty stoked on the inverted kingpin talk, as I've put Grind King kingpins in my thunders, and it would be rad to get a set that already had the work done and are actually designed for the inverted kingpin. They've got so much kingpin clearance!