I, too, share your dislike for the Lyman GPR sights.
ToTW and other ML suppliers shows several suitable front/rear sights. My preference is to modify the new sight dovetail to fit the Lyman, rather than opening up the dovetail on the barrel. These sights are raw castings and will require some clean-up work on your part.
I'd buy several of the sight(s) you choose as I sometimes take too much off the dovetail, resulting in a sloppy, loose fit. Start over!
Fitting the new sight dovetail to the barrel is a cut-n-try process. File a very slight taper to the sight base width, try it in the barrel dovetail, I like it to go about 1/4 into the slot, then use a brass punch for the rest of the way. Keep in mind you may want to move the sight(s) left or right to center the group.
There are numerous instructional videos on fitting sights, mostly on sites that illustrate building a ML firearm.