[Kevin Sevcik]

Didn't bother measuring it, but completely subjective testing in a P60 suggests no significant warping. It felt slightly rougher than a virgin one, but my hardened plate was already slightly bowtied and deformed from the above mentioned shocks.
Also, 20 minutes encompassed the whole heat treatment, including a 5ish minute soak at something above 1550F/bright red. Don't be knockin' my butane iron/torch.

Before anyone tries this for realsies, I'd recommend a little more research on someone's part. Possibly mine. I'd like to know the actual alloy so I can figure out a real heat treat procedure for it, including a temper. I said 40+ HRC for a reason. I tested multiple locations on the thing and my haphazard heat treat gave me hardnesses ranging from 40 to 60. This does not inspire confidence, and I'd really recommend a good tempering to relieve some of those stresses and reduce the chances of fracturing as your exciting new failure mode. Brittle fracture is obviously an even worse failure mode, since you've moved from a gradual semi-predictable failure to an instant an catastrophic one.

Finally, you're going to want to harden to shaft as well if you're expecting this to increase the life of your transmission. A stock transmission fails by deforming the shaft as well as the plate.