OK, another update.
To avoid any "hard to tell from pictures" here's video of what it looks like:
Maybe this will help to understand the predicament.
I did oil change today.
No, there is no SIDE access fill plug. Only regular transmission case bolts.
Plug at the top indeed is fill plug.
No surprises to remove filters, only odd head 2 bolts per plastic cover - 3/8, while the rest of mower is metric. Whatever.
Surprise was how little oil drained out and how little oil went in. Manual says "
Fill approximately 2 quarts of Toro HYPR-OIL® or 20W-50 engine oil to the
level of the top port plug hole.". It took in maybe 1.5 qrt with new filter. And, I did purge procedure, opened plugs again, and added a bit more oil, as it dropped down after purge, and purged again.
Right transmission had quite a bit of metallic milkshake in it. Donno, maybe because of my property layout, I take more right hand turns, than left hand. Donno. But glad I did change.
I used Toro HYPR 500 oil said to be good for 500 hrs from today on.

Total time took about 2 hrs actually. Oil drains rather slowly. Also, had to use narrow funnel to get inside the fill hole at the angle and had to literally trickle oil in.
Then, purge procedure, open plugs again, add oil, purge again.
For purge procedure, manual says to jump seat sensor but my mower was on 4 stands, so I simply set in the seat. and purged it.