I’ve never worked on a Lumina, but I had similar difficulty getting access to the bolts when replacing the starter on my Corolla one time. I had to experiment around with tool configurations using various length extensions to finally figure it out.
If you don’t mind a little story OP, one time my golf swing went to pot so I took a golf lesson. The instructor watched me a while taking swings, then said “George, there’s a lot of rules in golf telling you to not do this, and not do that, but one thing you are still allowed to do is aim.” Turned out my problem was I was concentrating on what not to do rather than what TO do. All I had to do was adjust my body position to aim where I wanted the ball to land, and that corrected my swing problem. lol … What I’m saying is that when working on cars to remember you are allowed to remove the wheels and turn the steering wheel to get access to the bolts. Even remove the axle shafts if you have to. In the case of my Corolla, in addition to the right length socket extension, which was different for some bolts than others, also I had to remove some of the under-englne shields, and turn the steering wheel in various direction to move stuff out of the way of where I wanted to place the ratchet.
According to what I’m seeing, for a Lumina w/the v6 3.1 L, the recommend procedure is to
- remove air cleaner ass’y
- remove oil filter
- re-position hose adjacent to starter
- disconnect starter brace from AC compressor
- remove brace
- remove flywheel inspection cover
At that point you should be able to access the starter bolts. Apparently you lower the starter a little first, then you have access enough to disconnect its electrical harness. Note that there may be shims installed, so watch for those and make sure to put them back where you found them on re-install. Best of luck.