The easiest way would be to acquire a real Mac OS CD. That model is roughly the equivalent of the Power Macintosh 6200, and requires System 7.5.1 or later. You can download System 7.5.3 as a multi-park disk image, but then you have the problem of getting that bootably onto the Mac, so finding an actual Mac OS CD (7.5.1 or later,) is your best bet.

eBay has them often. (That Mac will run 7.5.1 through 9.1.)