Spend some time looking through this thread. Page one post #8 may help you quite a bit. It shows the bulb locations.
https://forum.ih8mud.com/threads/definitive-led-thread-for-80s.213060/#post-3176818
Correct. 3 oem bulbs. When you pull the hvac controls you will see where they go in the back. Pretty sure there’s black tape over the openings where you access the bulbs.
The box color in the chart indicate the factory bulb color. Twelve 3mm green leds and two 3mm yellow leds for the on...
There are only three easily replaceable bulbs in the hvac controls. The part numbers are listed in post 5 of the thread I linked above.
There are other 3mm bulbs in the chart for hvac but those are soldered in place in each button and I wouldn’t recommend messing with them.
Post 402 has some tables with bulb info. It doesn’t have oem part numbers but you can match bulb sizes with the thread you posted and see what works. Or you have all the info to go led.
https://forum.ih8mud.com/threads/definitive-led-thread-for-80s.213060/page-21#post-12707494