If you do the glass block window flush with the wall, you don't need to shorten the shower. You can leave the plumbing in place. Look into a solid surface shower. This is Corian, Swanstone, Kohler Choreograph, Transolid, and more. You can install it over old tile after sanding to take off the gloss. Look through this thread on Houzz to see and read about these showers. ["Kohler Choreograph?" thread that covers a lot of SS Showers.[(https://www.houzz.com/discussions/kohler-choreograph-dsvw-vd~3420698)
A solid surface has no grout, so does not mold or mildew. It is a smooth surface that cleans easily. It is harder than fiberglass and will last for decades. It now comes in many colors; solid, speckled, and swirls that approximate marble. You need to have an installer who can scribe a panel to fit your irregular wall (almost all walls are not quite square) and who can manipulate a large panel into place that has construction adhesive on the back, who can calculate where to cut the plumbing holes. My Transolid shower back wall came in smaller sheets than the common full-wall sheets of most other SS brands. You can see it at the bottom of the thread I linked above. Here is a teaser:
Your shower drain can stay in place if you use one of the Kohler cast iron pans with side drains. Kohler also makes less expensive fiberglass pans that are well thought of. If you are saving money by not moving the drain, though, go for cast iron. It will last!
34 x 60 Kohler Bellweather in White
32 x 60 in Ice Gray
Kohler sells aluminum and teak covers to fit over the wells in these shower pans so that the floor is more level.
They also make this kind of fiberglass pan that matches their Choreograph walls.Proper installation of a fiberglass or solid surface pan is to put it into a wet bed of material such as tile mastic. That fills the voids and keeps it from flexing and cracking. So make sure you have the manufacturer's instructions on hand and that your crew follows them.
These showers are also available in the 42" and 48" sizes, but you will have to move your plumbing for a center drain for those pans. It becomes a choice between additional storage and a smaller shower versus less construction and no new storage. Only you can decide which you prefer.
Here is a 48" pan from Transolid on Houzz, but it is 34" deep. Chances are that your shower is 32" deep. Do you have room for a 34" or 36" depth shower pan? Most pans in the smaller width are going to be the larger depth.Swanstone goes down to 32 inch depth. Don't trust the colors shown on Houzz, They are not correct. Check the colors on the Swan site. Here is a 48 x 32.188 pan.Swan Veritek is NOT Solid Surface. It is probably fiberglass. Just be aware.
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