OK
When we are doing panel replacement whether it be quarter panels trying to splice them up into the Sail area by the back window or cutting them short and splicing them with an overlap at the dished area next to the upper peak on the top of the quarters. We have to do things in a manner that works for us as the assembler, as the car is already put together and we have to open it up and put our parts in.
So it looks like it is going to take a little modification in the area where the windshield pillar meets the cowl. I would say that the windshield A pillar is already down and welded in . . so no slipping the cowl under it now. I would say that Drop Down lip on the end of the cowl needs to come off, then you fit the cowl to the windshield pillar and Butt Weld them together in that area instead of trying to slip the cowl under the windshield pillar like the factory did.
So the tricky part is trimming back the end of the cowl drop down with an aviation snips 1/8" at a time then check the fit. Keep trimming it back 1/8" at a time and fitting it until it drops in and starts fitting right. Can probably do one side at a time and get things close. Then do both sides at the same time at the end to get a good final fit.
It is real easy to get it too short as things start dropping down into place so take your time. Worst case senario if you end up with a 3/8" gap there at the end, you will have to cut a little filler strip of body steel and wire feed weld it in . . then do your filler work over the top.