A photo of the whole mag might help. It looks to me like, if they are 9mm, they might be STen mags. They could be M3 "Grease Gun" mags if they take .45 ACP rounds. Both have the wraparound part at the top with the bump that bears against the magazine housing when the mag is inserted. The 9mm conversion for the Greaser evidently used STen mags.
M76 mags are similar to mags for the Swedish "K" but I think the butt ends may be different.
It's been years since I shot an M76 but I got to shoot a "K" last summer.
They do not look like the mags from my 76. The mag walls for that are straight in this area and the shape is triangular looking from the top. I can't tell from your pics how the mags are shaped.
The S&W 76 magazine is very similar to that of the Swedish Kulspruta Fyrtifem (K45) and the Finnish Suomi SMG, but both the K45 and Suomi stick mags require some slight modification to fit a S&W 76 or MKS760.
Below are photos of two known variations of production S&W 76 mags; the only difference is in the baseplates:
For those wondering what a Model 76 is, here's a photo of mine, fitted with a modified blued Suomi stick magazine:
It's a 9mm selective-fire submachine gun made in the late 60s through the early 70s. A little more than 6000 total were made. The S&W 76 is classified a C&R.