For what it is worth I just did this and so far I am very happy with the results. Removed the very old metal frame windows from my 1971 Ericson 29 and replaced with Acrylic bonded to the outside. I have not launched the boat yet so can not comment on the long term results.
I bought the acrylic from estreetplastics both cut very close to the size I needed and then a larger sheet I cut what I needed out of. I found cutting with a saber saw with a good metal blade worked well. Then sanding the edges with a palm sander. I did not put a bevel.
Old windows removed and then scraped and sanded to remove all the old caulk and gunk and cleaned with acetone. I sanded the inside edge of the acrylic to give the adhesive a better surface to bond to.
Dry fit the windows and then taped around the perimeter giving about a quarter inch extra. This allowed me to smooth out the adhesive and create a fillet around the windows since I did not bevel. I applied the adhesive and used the Dow 739. I was able to find a local distributer from the Dow Corning web site. Advertised as a plastic adhesive and seen another recommendation here for it. The data sheet on the Dow site reinforced my choice.
It was very easy to work with and dried to the touch within an hour. I didn't need to clamp as it stuck pretty well on its own. My hull has an extremely slight curve to it so did not have to flex the acrylic much. Smoothed out the edges of the adhesive around new window and removed tape.
You will regret the things you did not do, more than the things you did.
Get out there!
Saco Bay, Maine
1971 Ericson 29