Welcome to the forum.
I'm not expert so we'll have to get more opinions and suggestions from those more informed than I am but I think your chassis is a G30, correct?
I agree with
donr103 about accessing the air filter through the dog house or interior ...I'm guessing though.
Here is a video of somebody doing so in a 1994 G20 which I suspect could be at least similar to what you'll have to do ...still a lot of hassle just to get to the air filter but there are a huge number of G-series vans and cutaways out there so you won't be alone: