I did my the dash on my 68' 300 so cannot comment on pulling the windshield. I can tell you it took me about a year to get it right and mine was quite minor. The problem I ran into was experiencing the various expansion/contraction properties of the factory covering and this (or any) repair material. I would apply according to instructions, light sand to what felt level. Then over some days of leaving this project and attending to other work, I noticed the areas of repair would be raised or cracked. I could only relate this to a temperature change. Over the course of time, I would patch, sand and place in sun and in cool garage , eventually winter. I almost gave up on it when I placed it outside in the sun and the repair points raised yet again. I sanded smooth, primed again, painted, placed in the sun again, no movement. Thought I better wait for winter to see if it would contract and so far, no issues. I am still working on the rest of the car so "no real world out there kind of experience" however happy so far. I did purchase a cover to place on the dash to not push my luck. Polyvance video makes it look quite easy. Other thing I would recommend is using the flexible primer and paint. I could not tell if the material shifts were from original dash covering, putty, primer or paint but suspect they all need some flexibility due to temp changes. If this is going to be fun car show driver then would probably try again. If the dash is for show stopper, 7-10 grade kind of thing, I would look at the professional businesses that recover dashes.