Would a 3.4L 04 Chevy Impala motor fit 98 Venture?

No, a 3.4L engine from a 2004 Chevy Impala will not fit a 1998 Pontiac Venture without significant modifications, and likely not even then. The engine bays, mounts, and ancillary components are different enough to make it an extremely impractical swap. The 1998 Venture likely uses a different engine family and transmission, and adapting them would be a major undertaking, likely requiring custom fabrication.