1969 Saginaw 3-speed, no drain plug?

[Luke87gt]

Hi guys, headed into the garage this afternoon to change the transmission oil (1969 c10, 3OTT transmission) - 80w-90 gear oil

I get under the car and to my surprise, I don’t see a drain plug? There is a fill plug. I guess the early Saginaw 3sp transmission may not have had a drain plug?

What then is the recommended method to change the oil?

Also, I notice that one of bolts (transmission to bellhousing) has a snapped off head. The fun things you discover when you buy a 56yr old vehicle.

Thank you