[dak0ta]

Hi,

for my 870 express, will putting a sling plate between the mag tube and mag cap i.e. wilson combat, and another one for single point slings between the receiver and stock be enough to support the shotgun for a 2-point sling?

[dfariswheel]

Certainly.
The between the receiver and stock types are plenty strong, as long as you buy one that's not thin, cheap metal.

The magazine mount system has been around a long time and works well.
While it "can" pop the magazine cap or extension off if you apply a hard enough yank, this takes a pretty big yank.
Another option is one of the Uncle Mike's type sling swivel sets that mounts a sling swivel on the end of the magazine cap.
Since the cap screws on the full depth, it's even stronger than the between the cap and magazine type:

http://www.unclemikes.com/products/remington870express.html

And you can replace the standard swivels with Mil-Specs.

http://www.unclemikes.com/products/mil_spec_swivels.html