91 Suburban 5.7 4L80E

Soon I'll be changing the tranny filter out and replacing only the fluid lost from the pan. No intentions of a flush, the fluid looks and smells good, and the tranny is working fine, just a preventative maintenance measure. However, the pan doesn't have a drain plug and I'd like to install an aftermarket plug kit.
Where should I drill the hole? It looks like there is a slanted area that would be perfect for a plug, but would it be better to go straight through the bottom?
Theres a circle on the bottom of the pan that holds the magnet, so I'll stay away from that.
Small issue, but wondered what other people thought or their experience.

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