Husqvarna/Williams receiver sight?

[Grouser]

My father had a 4100 lightweight (1950"s) and it was drilled and tapped for a receiver sight. He had a Williams Foolproof installed. The gun is long gone and I came across a good one and thought I might set it up the same -- anyone know what number/model Williams will fit it?
Thanks in advance!

 

[Bassmaster]

You can prolly get the info you need directly from the Williams web-site....
The FP-98 will prolly work