I've got the lyman peep for the 1886 on my '95, so my guess would be the '86 in the Williams would be the one you want. Give Brownells a call, they will help you out with it.
http://www.peabodyrifles.com/ They have the repro of the model 21 Lyman, another option. If I had do do it all over again, an Ashley ghost ring would be it. While I still like the lyman and Williams, I've mounted Ashley ghost rings on a couple of other levers and am finding myself prefering those. Although if your looking for the "period look", the ashley wouldn't be the one. CRASH87