This was discussed in another thread. http://www.marlinforum.com/forum/f6/336-replacment-sights-887/
As I stated there, I am not an expert on this topic. However, I mounted an XS Ghost Ring on one of my 336 Marlins and was less than pleased. It came with a small and a large apertures. I found the smaller one to be too large. It would have worked well on a shotgun but not for the accuracy that I desire from a rifle.
My suggestion would be for the Williams or Skinner. Although I've not owned either, that is where I would look first.
Just my 2 cents. And yes, just like the XS, I'm sure that they can be ordered to mount to your scope base holes.
Hope this helps. I'm sure someone else will chime in.
Welcome to the forum bowman.....
The Skinner sights have a set you can mount on the top and Williams has a model that attaches at the pre-drilled holes on the side. Both of them work well. It really gets down to personal preference. All the online places like Midway, Grafs or Natchez carry the Williams. Here is a link to Skinner. http://www.skinnersights.com/3.html
Hey Bowman; welcome to the forum and check the link that greyhawk listed, that peep sight is a" Williams" from Midwayusa.com @ $30+ bucks it goes right in the scope mount holes and I had to change the front sight as well, a Williams gold bead (1/16") .406" height I believe, also midway $12-$15 bucks. I'm getting 4" groups @ 100 yards. That rifle will print 2" groups with a scope.
Williams offers one that mounts on top of the receiver in scope holes. It is the WGRS. That one sits high enough you may want to get their set which includes an appropriate height front firesight bead.
They also offer the 5D or FP with mounts in pre-drilled holes on the side of the receiver, or a model that mounts in the scope holes too. If yours is new enough that the holes aren't drilled on the side of the receiver then the FP336 or 5D336 model is for you. These too are offered in a set with an appropriate height front firesight.
Skinner makes some pretty slick looking models for Marlins. He offers a choice of stainless, brass, or blued steel. He can also make a pretty good recommendation for a matched front sight. I like his front sights a lot. They are narrow with a square top surface which seems to give a sharper sight picture than the firesights which kind of give off a round glow that may be less precise. Unless you need the illumination in twilight hours the sharp plain post may be your best option.