New windows bedded in butyl won't leak, but your eyes might when you get the price.
Those look like the ones fitted to my Snapdragon, which I had refurbished a couple of times to no avail. They had frames in an h section, where the Perspex went into the bottom n. What finally worked was to cut the h down to form an l and get Perspex sized to the outside dimensions of the l, which was now just a trim. On the inside, I made thin ply trims and bolted through everything - ally trim, a self-adhesive neoprene, butyl tape, cabin and trim, finished with domed nuts.
From the outside, they were indistinguishable from the originals from a few feet away, and looked pretty good on the inside, too.
Best thing? No leaks!
It wasn't difficult to do, but you have to enjoy fiddling and fettling!