I got it this time.
If the chassis is level with the floor all around then the body should also be level with the floor. I trimmed any interference as I lowered it over the chassis. I had the body on blocks so I could get all the measurements even before I started welding. Get the two front corners even side to side then the back. Check inside from the doors to the center of the floor. Then check everything again before you weld. I would tack weld as many locations as possible then measure again before making it final.
It took me 3 or 4 days to do it taking my time so you're right on schedule for a first timer. Good luck. Keep us posted on your progress and post the pics as soon as you can. You can get 35MM pictures put on a CD when it's developed by a Kodak lab. They look better on a computer screen than a scanned photo. I used Rite-Aid drug store If you have one near you.