I also have '95 3.1L Lumina sedan and replaced the starter a year or two ago.
Don't worry, you don't need to remove the oil pan.
Just... (These are from memory mind you.)
• Disconnect the battery.
• Remove the wires from starter
• Remove the small metal inspection plate on the bell housing at the front of the starter.
• Remove the plastic oil filter drip guard from under the oil filter.
• Remove the two bolts holding the starter on.
• Lift starter out from the top.
[Reverse to install.]
There wasn't quite enough clearance around the starter to drop it down from underneath. So I removed the oil filter drip guard to get the necessary room to lift it out from the top.
The biggest pain of the whole job was holding the new starter up while trying to align the two mounting bolts with their holes. Other than that, it was a piece of cake.
Cheers!