OK mate, you can get away with leaving the side wall 'rack' in place, as it can pass for framework, but you'll still need to remove some of the floor equipment if a seat is to be fitted.
Now, the instrument panel. It's up to you which way you paint it, but, the starboard side has a panel that needs to be folded up, or cut off, as shown in the AM sheet. I found it better to cut it off, then glue to the side console on PART 30A.
PART 31A shows the bottom section needs to be folded up 90 degrees. this is almost right, but pics of the real thing show that this side console slopes slightly. Fold it, glue the part in place, then fix the folded part with CA glue underneath, otherwise it'll want to 'flop' back down again! This will make more sense when you see the AM sheet, and combine it with the Italeri sheet. I'll log out now and try to e-mail the AM sheet, but it might take a bit of time with this bl**dy slow 'net connection!
BTW, there's some colour interior shots on the Kiwi Wings web-site that are useful, mainly for the pilot's cockpit, but bear in mind some of the original equipment fit is missing.