Auto gearbox, drain, and refill

1990 3.6, car

While it's all in bits, I'm getting all the other little jobs done.

The exhaust is off completely, so access to the gearbox is easy.
I want to drop the sump(?) and clean the filter, check for debris. as mentioned by a few other posters.

Is this straightforward?
Are there any little problems or things to look out for?

Working space will be limited. Basically just enough room for me. The car is currently on Axle stands.

Issues with the box-
There is no gear display. Either on the Dash or by the gear selector.
The 3 position switch does not always return to econ when starting.

Otherwise, all seems fine. The oil that I drained didn't appear to be overly blackened or contaminated. It seemed fairly reddish in colour once drained. About 4 litres or so came out.