The Aimtech Warhammer Tactical Mid Length Saddle Mount should work fine with that model 590. The heat shield will be replaced and the sights should be comaptible.
The Aimtech Warhammer Tactical Mid Length Saddle Mount will not fit a 20 gauge Mossberg Maverick 88.
The Aimtech Warhammer Tactical Mid Length Saddle Mount cannot be guaranteed to fit that shotgun.
Yes, Code:A9-T8-AWBRM-ASM-3MD should be compatible.
This may not be compatible, we recommend reaching out to the manufacturer for conformation of fitment.
It is not likely that the clamp will fit a breacher barrel, although the manufacturer does not list compatibility for barrel types.
Please email us at techsales@opticsplanet.com so we may further assist you with your issue.
The models listed on this page are only for 12 gauge. For the Mossberg 500 20 gauge model that will be compatible with a Maverick 88 20 gauge you will need to go here: https://www.opticsplanet.com/aimtech-war-hammer-tactical-rail-mount-moss-500-590-20ga.html
Yes, this would fit.
No, this will not be compatible with a vent rib barrel.