I’m sure you already know this, but I’ll provide it nonetheless. One of the bolts on the starter is only accessible from the interior of the car on the transmission tunnel access panel. It is high up on the tunnel in the passenger footwell. Four screw hold it in position. Other than having to tear out the carpet section on the tunnel, it is easy to access and get the screws out. You will see one of the starter bolts (the lower one) and it comes out fairly easy.
The top bolt is visible on the starter right near the firewall. In my case, I used the longest wrench I had to break it loose, then used a shorty wrench to turn it 1/8 of a turn at a time until it was loose enough to grasp with my finger.
As for the air filter, it comes our fairly easy too. The black vacuum tank takes a bit of messing around to get out. In my case, I had seven bolts holding the black floor section on under it. After removing that floor section, I was able to get to the rear two bolts that hold the vacuum tank with an obstruction wrench. Once those two bolts were out, the front two are a piece of cake.
With the vacuum tank out, I was able to reach in with two hands and grab that monster Lucas starter. In your case, if it is an aftermarket starter, then it should be easy to navigate it out.
Just a hint, make sure you have completely disconnected your battery, especially the positive terminal on the battery which goes directly to your starter. Taking the black/ground cable off isn’t good enough.