I recently purchased a .36 caliber Seneca. I love shooting this rifle! Like you, I ran out of downward adjustment with the factory sight. I never liked the factory modern looking adjustable sights, so I easily made something a little more traditional looking.
For the front sight I ordered a blank from Track of the Wolf. Part #FS-TC-BB-80
From there I reshaped it and left it plenty high to make adjustments if needed.
For the rear sight I had to get a little more creative, because I didn't want to cut a dovetail in my barrel. I wanted to be able to put the factory sights back on, if needed, for resale value.
I recently put a scope on my Glenfield Marlin Model 60 .22 rifle. So I had the rear sight in my parts drawer. These rear sights can easily be found on eBay for around $20.
I used my Dremel to cut off the dovetail part on the front of the sight. I then reshaped the front to a point. Then I used the cutting drill bit to make a larger slot at the front of the elevator ramp opening for the mounting screw (these spring steel sights are impossible to drill a hole through). I then measured the distance for the rear screw (mine is an early barrel with the closer screw spacing) and used the bit to make the second slot. I used the original sight base screws to mount my new sight and indexed the slots so they aligned with the barrel. Lastly, I cut the front of the elevator ramp off so that it would fit in the opening.
I am really happy with how this new sight setup works! The new rear sight is solid! No more wiggling factory boxy rear sight. Windage adjustment was made by moving the front sight in the dovetail. Elevation was adjusted by filing down the front to bring the point of impact up (this new rear sight was lower than the factory one).
I sighted the rifle in with the elevator ramp in the first (bottom) notch, so that it is dead on at 25 yards. I can then use the ramp to adjust elevation up if I need to shoot longer distances. It works great!
Plus, I think the new sights are much more period looking and give the rifle a more traditional feel.