Video reference, TF727 600hp rebuild

I watched one of the videos; the direct drum assembly. There are errors. NEVER machine the inside of the drum if it's scored from ring wear. It will be too big and the rings won't seat with enough pressure to seal on a hot SoCal day stuck in traffic on the 91; you'll fall out of high gear. This five plate setup is fine for 600 hp, but seven plate assemblies are available for under a hundred dollars.
How do you explain the operation of Teflon sealing rings then?
They have almost no tension at all and yet they work great.
I would say it is safe to machine the drum if it's not severe.
The video did not say how much stock was removed.
Probably a few thou would be fine. IMHO