I am ordering a Lyman 66 for my Browning model 71. I also will need to replace the front sight. How do you know how high of a sight you will need on the front?

If you have or can find a Brownell's catalog, the formula for determing what you are after is there. I don't remember it off hand, but it's not complicated. Not sure you will even have to replace the front sight blade on the 71. I have 71's with Williams Foolproof receiver sight and works fine with issue front sight blade.