Have you tried output=opengl with aspect=true instead?

That just doubles every 4th (5th?) line, creating some ... interesting artifacts. My method gets the proper, same-size (rectangular) pixels.

But your method sounds much simpler and safer.

opengl output does not double lines, it uses bilinear resampling.

Something like:

Fullres=orig
output=opengl

aspect=true
scaler=normal2x

?

Gave me 16:9, not 4:3. Am I missing something?

Don't use fullresolution=original, set it to desktop or whatever the native resolution of your screen is (or tell the nvidia drivers to preserve the aspect ratio, not scale-to-fit).

Ah, that seems to do the trick.

Man, dosbox is complicated....