Welcome to the forum!

Purchase optics with a good lifetime warranty and quality construction/materials. Personally, i would not scope the gun for the purpose you describe; but you need to choose what is best for you. It all depends on what you want. As to brand or model, you will need to look at the optics yourself to see what you like.

Be aware there are material differences between some of the factory offerings in the 45-70. Some factory loads are lower power to be safe in Sharps replica rifles.