870 Express Reciever and Weaver Base Scope Mount

[east_coast_angler]

Good day 870 Users,
I own a Remington 870 Express Combo. I wanted to mount a red dot on it this year to shoot Hornady SST slugs, using the rifled barrel, this year for gun season. I wanted go with the permanent more solid option and gunsmith an aluminum base on. I researched this base on the weaver optics website. http://www.weaveroptics.com/rings_bases ... slot_base/ it recommend that I use the 48345 MULTI SLOT 870 REMINGTON. So that is the one I purchased. When I received the mount. The first this I noticed is that the underside of the base is completely curved, and with that being said, the Remington 870 Express has a small strip flat surface on the top of the receiver. Will this still mount properly? Has anyone else had this problem and what did you do? Should I contact Weaver? Ive never owned anything other than the express, does the wingmaster have a completely curved receiver without the flat part on top of it?

[Synchronizor]

All 870s that I've seen have a flat on top of the receiver. It's used as a sighting plane, a sighting clearance, or a scope base mount surface, depending on the configuration.

Apart from the flat bit, does the rail fit the curve of the receiver well? If so, I imagine it should work fine.