Can you give us a model number?

If it looks like a Marlin, it probably is. Marlin made 30-30 rifles for Sears (and so did Winchester, for that matter).

If the rifle's been well-maintained, it'll be safe to shoot. That's what rifles are made to do. Some guy over on www.marlinowners.com hunts with a Marlin that's about 100 years old, if I remember correctly.

In terms of potency, you'll find a lot of people who hunt deer exclusively with a 30-30, and do just fine.

Will you be using the rifle for deer, or have you maybe got feral hogs in mind?