Two things.
You can cut the side ribs where they are straight and cut the four corner ribs higher at least 3-6 inches above the windshield and the ones in the back where they work for you.
The only difference between a regular roof raise from the whole enchilada raise I see is that where you cut the front and rear caps?
You would have to cut that skin at an angle to match the window cuts where the skin is removed and do some metal patchwork on the four corners when the raise is done.
A roof raise means you gotta jump into metal work anyway with the skin replacement to fit bigger windows and the same jig saw,grinder,whatever for that can be used for the corners. Bar clamps,c clamps, will help a lot.
Most busses only use 15-16-guage skin so clamps will do the job.
For the ribs there are many options but they an either bolted,riveted,screwed,or welded.
Several options.
I know you are going to remove the side windows but please protect any glass you want to keep cause grinding/welding sparks or anything like that lose to a piece of glass will stick into the glass.
Don't give up?
Just cause your not ready to weld doesn't meen you can't do a raise?
How many welds have you seen in your bus?
There is zero on mine.
Everything is bolted,riveted,or screwed?
Why do you need to weld?
I have welded. Almost daily for over 20-years and so for my bus has not even been touched by my machines. Everything is bolted,riveted,or screwed and most screws used were the same ones I took out of the interior panels.
Good luck with your decisions. It is very doable without ever touching a welding machine.