The safety inspection people here started by telling me I needed to install side marker lamps, but my car has beehive-style tail lamps and matching front lamps - which the inspectors here accepted as they're visible from the side. Do they meet the viewing angles as defined in DOT specifications? Unlikely, but they were still accepted.
I also had to install reflectors visible from the side, but was able to source 2" x 3.5" self-adhesive mylar reflectors that are attached to the side of the bumperettes - amber in front and red in rear. They look like this:
If my car had rectangular tail lamps and/or lower profile front lamps then the discussion likely would have been somewhat different.