A 19" PC monotor is smaller than a 19" arcade monitor. Also, unless it is a very old monitor, the curvature on the PC monitor will be less than that of an arcade monitor, maybe none at all.
I use a 19" arcade bezel from Happ on a 21" PC monitor, but I had to custom-trim the curves to get it to fit. I use a thin line of black foam weatherstrip between the monitor and the bezel to fill the imperfections in the fit.
Note that most "classic" arcade games used a simple cardboard bezel. See
http://forum.arcadecontrols.com/index.php/topic,17175.0.html for instructions on how one is constructed.