Liking the Exec. shuttle variant.
For reference, here are images of my model kit I put out through Federation Models.
Lovely….I might have Raan nacelles with supports curving out and down from where that F-18 cutwater/ Leading Edge Root Extension (LERX) is at its widest.
Maybe for a later larger design…maybe have an additional deck atop the manta half way out to the pylons..an another atop that only a third of the way out for the shuttlebay/powerpack to rest on…