if youre interested van Me and my brother did his 57 4 door in 4 sections. Came out pretty sexy. It takes a lot of Jig-Sawing to get it perfect but i'll post pics if you have any interest.
When I chopped my 55 Caddy, I cut 2 3/8 " outta the windshield and 3 1/8 outta the rear. Porta powered the upper roof nubs out and used a chain come along to pull in the cowl nubs. Welded it up and drove 3 hours to a glass guy who belt sanded 0nly 1 windshield and had it done in a day and a half. I never even took out the headliner. I did the whole chop on a 3 day Easter weekend myself other than help lifting off and on the skin.
I will be chopping this 56 by sinking the windsheild for sure. I am confident that I have gathered enough info to get it done correctly. I will post pix as I go. Maybe do a complete how to but I would have to save that for tech week...came in 3rd on the last one I tried. Maybe 1st this time???