Weaver makes a 2 piece base that fits factory drilled and tapped 870, 1187, 1100. Stock # 48346. I just picked one up at Wallyworld for $6.00. I see alot of people buying the full weaver rail and then cutting it down. This is a simple solution. I'm gonna be mounting my FF2 using the pictanny/weaver to my 870.
Thanks for the info J.