Bought a 2531.80. The anti-mag cover doesn't have any engraving. Is it an actual anti-mag cover?

Hello, I bought a 2531.80 from ebay. It said "recently serviced", and it is running well (about -1s a day). I opened it up because I'm comfortable doing so, and have put together a few custom watches myself. This is the 3rd Seamaster with 1120 caliber I've owned. This is the first time I've had one with a blank anti-magnetic movement cover. It also weighs almost nothing. 1g on the scale. Is it a real antimagnetic cover? Or is a real iron cover heavier? I feel like I might have overpaid and afraid I was scammed for the promise of it being genuine, serviced, with box and papers. Please let me know if you think this looks ok.

Thanks, Appreciate the help
Dave

Looks like it. So assuming it’s genuine Omega cover but just from a speedmaster?