Vintage Constellation case in poor condition

Hello everyone my name is Cesar and I’m a novice watch collector and have started to collect Omega vintage. I just bought a vintage constellation that needs a little attention. The crystal needs to be replaced and it appears that the case has lost its plating or someone removed it and tried to polish the case. I’m wondering how to open it #1 and next is trying to find another case or re plate the current one. Are these top load watches or a split case any information would help. By finding the case # I can start the search and get my watch going. Hopefully the movement isn’t rusted but I can hear the rotor moving when I shake it. I cleaned the crystal a little and I like the dial so far. I’ll keep you all posted what movement is inside and the condition as I get this watch going. Thanks for any positive advise.