I would give XS sights a call on Monday and see what they recommend. They are great people to deal with and very friendly. I expect they can recommend the proper height front sight for your application.
Welcome to the forum. Good advice was given on how to adjust the rear sight. I have an SBL and its a tack driver. Take her out again and try different types of ammo or if you reload try different powder and bullet charges. These thing love to be pampered by their owner and they most certainly have a sweet spot for a certain bullet and velocity. Good luck and let us know how your coming along.
All advice on elevation is good. If you’re maxed out, you may need a taller front ramp. One more issue with windage adjustment. I have an 1895 SBL with Skinner Trapper sight. The forward mounting hole, on the receiver was tapped .024” left of center on the bore axis. This introduces parallax at distance shorter or longer than your zero distance. The logical fix would be to send it to a service center and have it redrilled. There isn’t much room to do this. My fix was to have a machinist slot the forward hole in the sight base, similar to how the rear hole is slotted. This allows me to center the sight base and remove the parallax. Works perfectly. I will post a pick if I can figure out how.
Got the rear XS Ghost ring sight adjusted for elevation today, and very happy with the results! Still disappointed that a thousand dollar rifle wasn't at least hitting paper out of the box, but it's a moot point now. Much appreciation to the members of the Marlinowners group who gave helpful, positive, and encouraging suggestions - and a tip of the hat to JACKTW.
My SBL punched out this group at the lower left at 100YDS on the first trip to the range with Winchester 300 gr ammo. Did not use the iron sights though, this was with a scout scope I mounted right out of the box...
Forgot to mention to you that I sighted mine in with iron sights but my tired old eyes required that I use a scope so mounted one using the Leupold QD rings. Friends can't believe how accurate this rifle is. If I get into the right hunting situation I can remove the scope and use the irons. When I re-install the scope back into the same spot it never loses the POI. Love this thing.