Boxing at 160 pounds and below seems to be a sport dominated by rangy thin guys. Really every division below 200 has some element of that. But some guys stand out more than others. I see Tommy Hearns, Erik Morales and Alexis Arguello and those guys were rails. Arguello especially stands out though among this group. When he turned sideways I thought he was going to disappear.
Flyweight at 5'2" is kind of to be expected. Arguello was a Featherweight champion at 5'10". Even when he bulked up to LWW he still looked like he was going to disappear as soon as he turned sideways.
http://gloriagduran.com/wp-content/uploads/350px-brown.panama.al2_.jpg http://www.boxingnewsonline.net/wordpress/wp-content/uploads/2015/09/SandySaddler.jpg Hearns filled out more as he got older, but he was pretty damn skinny in his younger years. http://static.boxrec.com/9/9f/HKBDMag.8010.jpg
I suppose any tall guy who is at a lower weight. Hearns, Arguello, Foster, Tough guys to beat. You had to find a way inside. With Hearns and Arguello it took Hagler and Pryor forcing the action to get to them.
Antonio Cervantes at 5'9", 140 lbs, was no Charles Atlas. On their fight tape, he looks taller than Wilfred Benitez (though WB was only 17 years old at the time and may have grown some later.
Arguello came to mind immediately, as does Bob Foster. Foster, honestly, looks like I could break him in half but I have no doubt he could whoop my ass.
Nel tarleton , 30's british fw champ fought hof freddie miller twice ( close 15 round decision losses ) and panama al brown to a draw. He was never ko'd in 140+ fights . he did all this after contracting tb as a young child , leaving him naturally weak with only one functioning lung. Despite him falling short at world level , this makes him an atg in my book