This should do it. Follow step 1, but rather than changing ANYTHING at all, leave the window open. Continue to play D1 as normal.
Should you want to play in windowed mode, this will work for that mode. (Also stops the colors from fragmenting to hell (and back)!)

https://support.microsoft.com/en-us/help/14108/windows-7-change-screen-resolution

Haven't tried with d1, but to make d2 work properly I went into my vid card setting and set the settings to use gpu scaling and maintain aspect ratio. (so it won't try to make a potato x potato resolution try to fit on a widescreen monitor or stretch pixels)

Do u have multiple monitors? Like a tv above or something. Game may try to center itself between the two

play it in window mode, thats the ez and quick solution

Window mode = game crashes after you kill the butcher.

look into this, it's a diablo modded game that makes the game quite enjoyable and works amazing

http://diablo1.ovh.org/hd/

since you have the original diablo, just copy paste those files in the same folder and use the new .exe launcher