This strap was left off of the Meng kits as well as the Hasegawa kits and is a very prominent feature on all late F-4Es, Gs, Fs as well as FGR.2s and F-4Ss and others. It is an easy to install and will make a very accurate representation on your model. The set is 3D designed and printed in 8K format.
Always make sure to check your references for your particular model and time period as these were added over time, usually when the jet went to depot maintenance. They are simply a life extending airframe reinforcement plate.