Alright, for E1M8 I managed to fix the sky edges leaking into view, at least up to 16:9. Now the map works in DOS albeit still has some HOM effects :/.
Though not sure how to get the DGCTEX working in DOS.
Here it is: E1M8DGC3.wad
EDIT: @Wesbat, if I may ask, please update the UMAPINFO for E1M8 to be called “Ashes over Babel”