Howdy
I bought my old EuroArms Remmie back in 1975. At that time, all the 1858 Remingtons imported into this country had short front sights.
It always shot high.
When I decided to buy a cartridge conversion cylinder for it about 20 years ago the first order of business was to find a taller front sight.
I don't have a photo of it with the original sight, this is the taller front sight it wears now.
Here is are a couple of close ups of the 'new' (20 years old now) front sight.
I seem to recall I bought an Uberti front sight for it. The new sight did not fit the original dovetail, but it was a simple task for a gunsmith to recut the dovetail to accept the new front sight. I just measured this front sight, it is about .380 tall, measured from the top flat of the barrel.
I would go to VTI Gunparts. They have a front sight for the 1858 Remington listed for $13. Item number 15. Be prepared to take the revolver to a gunsmith in case the sight does not fit the original dovetail. The original dovetail on my old EuroArms Remmie was too small. With the new front sight I was satisfied that my Remmie was putting my rounds right about where the point of aim was. Sorry, I cannot be more specific than that, but with the new front sight I went ahead and bought the cartridge conversion cylinder.
https://www.vtigunparts.com/store/shopdisplayproducts.asp?id=13&cat=Uberti+1858+New+Army
I would not remove any metal from the top strap, the 1858 Remington frame is already pretty skimpy.