Time to add a Lyman 17A to my Henry 20" barrel with a Williams FP rear- What height Lyman should I start with?

thanks
chuck

I would suggest installing the Williams sight and shoot it with the factory front sight first. (perhaps you are doing this already) and see how elevation works out on that particular rifle. Make note of how much up and down elevation adjustment remains on the rear sight. Measure front from bottom of the dovetail to compare to the available 17A heights.

From the chickens to the rams you'll probably be raising your rear FP anywhere from 20 to 30 clicks maybe more depending on the ammo your shooting.
ppkny