Ashley Outdoors (now XS) and Wild West Guns both make good sights for the Marlin leverguns. The Williams Sights are nice but lack the style of these two designs.
As for a trigger job--I don't know of one that can beat the WWG drop-in "Trigger Happy" Kit. Haven't heard of an unsatisfied owner to date. I don't know if it will fit your particular Marlin, but Wildalaska (who regularly posts here) will know--he works at WWG.
I'm considering them too, although they aren't adjustable.
Actually, I believe they are adjustable. From the XS website in Rob1035's link:
"Ghost-Ring rear sight is fully adjustable for windage and elevation."
http://xssights.com/store/pix/catalog/rifle/rifle-gr-windage.jpg
Just for fun, here is the link to the WWG sight.
http://www.wildwestguns.com/Accessories/accessories.html
Here is the blurb about the trigger--you can find it by scrolling down from the top of the link for the sight.
"A precision EDM sear and trigger that is hand polished to produce a crisp, clean 2-3 pound trigger pull on ALL Marlin centerfire lever rifles. Unique patent pending design eliminates the infamous and annoying Marlin trigger flop. Now anyone can have the crisp, light trigger that has made our custom Marlin rifles well known all over the world. It's a trigger job in a package! Gunsmith fitting required. Available in Blue or Nickel."
I have heard of only one instance where very minor fitting was required in spite of WWG's caveat. It's almost always a drop-in installation. Mine was.