I replaced my windows in my 272. The screws are not there to hold the windows on. They are just there to hold the lexan in place while the Dow 795 black sealant dries. You could even remove the screws after installation, but no one does.
Insert a long putty knife and slowly cut the sealant away from the hull. It isn't easy because the seal is several inches wide.
And yes, Rudy at DR Marine has the windows. They are around $85 each. You could probably get them cut locally for less. DR Marine's windows require you to use yours for templates to match the screw holes.
Do NOT overtighten the screws! If the lexan is dimpled under the screw as you look along its length, loosen the screws. After the sealant dries, check it again. The only way the screws are too loose is is they are missing! Remember, the screws are superfluous onces the sealant dries.
I bought my windows at DR Marine, and they were perfect replacements, but a bit pricey. I will make my own next time.
Thanks,
Andrew