Will a small block 305 fit in 1997 Chevy lumina?

No, a small-block 305 Chevy engine will not fit in a 1997 Chevy Lumina without significant modifications, and those modifications would likely be impractical.

The 1997 Chevy Lumina typically came with a much smaller V6 engine. The engine bay is simply not designed for the larger dimensions and potentially different mounting points of a 305 SBC. You'd be looking at major firewall and potentially frame modifications, custom mounts, and a lot of other fabrication work. It's a project that's far beyond a simple engine swap.