Those look like RivNuts, which is more sound than threads into a thin-wall tube; I've replaced stripped threaded holes on aluminum sailboat masts with stainless steel rivnuts. They work sort of like expanding hollow-wall anchors (aka Molly Bolt), but stronger. However, the expanded head inside the tube, is not nearly as much area as a welded block, so any adapter mounted to the rivnuts is still not as strong, not in pullout strength, but in lateral wobbling of your front mount with cargo, and I might expect the head tube to fatigue crack around those holes. Perhaps not if the threads are only used in tension, and the mount stabilized with contact against the head tube itself.