I'm guessing the sight has already shipped. We really do try to keep the Skinner Henry "BIG BOY EXPRESS" sights in stock. They are VERY Popular, as are the Henry Rifles. I have a .44 Mag (pictured) and it shoots GREAT. Accurate, feeds like butter, trigger pull acceptable, no issues at all. How does the brass hold up? Just fine... You wont wear it out.
Front sight? As always, there are so many variants (Rifle characteristics, Load Selection, Shooter) we can't say for sure if a front sight change will be needed. (Mine needed about a .050" taller front sight with fairly standard Magnum loads and with me shooting it) Many customers report that it has worked with the factory front sight, others have needed a change. (Please see the first couple questions on our FAQ page and the STICKY titled "Will this sight work with my factory front sight" in the Skinner Sights section of the INDUSTRY PARTNERS listed here on Marlin Owners)
For what its worth.... EVERY Henry Rifle I own works wonderfully well. They are all accurate, well fit, have great wood, and Henry's Customer Service is A+++
ANDY