Mrs. Hoffmann was to replace her old existing mull windows.
She wants them shorter in height. The rough space is 149” long and 72”
In height. She has 4 37 x 63 new single hung windows she would like to use.
Allowing for the stud framing, she has no idea how much cinder blocks, if any
She will need to fill in spaces. See picture. Any suggestions?

So they will be 9" shorter?
And this is in FL, so you want to use as little wood as possible?
Do her new windows have specs with them about mulling and how much if any slope there is at the sill?

I think she doesn't want mulling with the new windows from Home Depot.
I guess it will need revisions to accommodate her desires ?

Are these new construction or replacement sash, big difference? Shouldn't need anything for the side, 1 block for the base. Window should state RO-Rough opening. Mulling goes between the windows to join 2 to make 1. Concrete usually forms the sill on windows shown, windows are bedded in concrete, not an easy replacement job.

Yes it is more involved. Currently the windows are 40 years old. The windows are set so low, you can step over the sill. The 37" wide windows, 4 of them would be 148" in the 149" space. That is considering the windows connecting to another without any spacing in between. The current windows are just to long in height
Thanks for the input