The drip rails are a pinch weld between the roof skin and the tubular bracket that runs above the window area. By cutting off the drip rail, you'll leave nothing to tie the roof to the car frame, without some serious welding work to be done. And that welding, if not done well, will warp the roof skin.
I did it to my 68 coupe... if you cut along the edge of the roof (insided the gutter) you will expose the two pieces of metal resting on top of eachother. The top piece it the roof, the bottom is the lower portion of the drip rail that goes into the door jamb area that the upper weatherstripping is attached to. I did weld these two pieces together and did not warp the roof. But I'm not to comfortable with the structual strength either since it's basically a weld on the outer edges of 0.030 thick sheetmetal.. not too sound in my opinion... It looks OK, but not sure how it would hold up in a collision.. If I had to do it again, I think I would have cut the gutter closer to where the lip is pinched over... this should leave the two layers that make up the bottom of the gutter. tack weld or better yet spot weld them to eachother in several places then fold them either up towards the roof or into the jamb area,... tack weld them up solid (like installing a quarter), grind the excess and follow up with some filler... I'm not sure how well this would work, but I wouldn't advise the way I originally did it... If you plan to do this, get a sawzall out and cut a section out of a wrecked mustang and try the various methods to see what works best... Also there is lead near the windsheild post and also near the rear quarter that you'll need to deal with... The shaved rail issue is one of the reason I'm seriously considering replacing the coupe roof with a fastback roof...
I am having serious deja vous. I saw this same question about 2 months ago on the forum....Maybe our fearless leader (admin Bob) would remember it and find it for you. It had pics too.
I do remember it Looked nice, but sounds scary to do.