Those appear to be Gen III LS 4.8 rods and pistons.

The pistons are for a Chevrolet 5.7L LS engine. The 121 casting number on the connecting rods is what's used on a Gen lll LS engines. Link is a discussion started by someone with 99L7++ pistons from an '02 5.7L engine.

References:

https://ls1tech.com/forums/generation-iii-internal-engine/1920112-piston-iden...

Reason:
Yeah, that's what I thought, too, but when I look up Mahle 224-3540 or pistons and rods for that engine, they aren't VISUALLY like these, the pattern of the rods are different, and the area on the heads where the bearings go is shaped differently. Do you think that matters? All the numbers match that engine, but I can't find any that LOOK like these.

here is a vehicle fitment 1997–2004 Chevrolet Corvette 1998–2002 Pontiac Firebird Formula, Trans Am 1998–2002 Chevrolet Camaro 1999–2004 Holden Special Vehicles Clubsport (VT, VX, Y Series) 1999–2004 Holden Special Vehicles Clubsport R8 (VT, VX, Y Series) 1999–2004 Holden Special Vehicles Grange (VT, VX, Y Series) 1999–2004 Holden Special Vehicles GTS (VT, VX, Y Series) 1999–2004 Holden Special Vehicles Maloo (VT, VX, Y Series) 1999–2004 Holden Special Vehicles Senator Signature (VT, VX, Y Series) 2000–2005 Holden Ute 1999–2005 Holden Commodore (VT, VX, VY, VZ) 1999–2005 Holden Statesman (WH, WK, WL) 1999–2005 Holden Caprice (WH, WK, WL) 2000–2002 Holden Special Vehicles Senator 300 (VX) 2000–2002 Holden Special Vehicles Coupé GTO (VX) 2000–2002 Holden Special Vehicles Coupé GTS (VX) 2000–2002 Holden Special Vehicles SV300 (VX) 2000–2004 Holden Special Vehicles Maloo R8 (VX, Y Series) 2001 Opel Omega V8 (prototype) 2001–2005 Holden Monaro CV8 2005 Holden Monaro CV8 Z 2001–2005 CSV Mondo 2001–2013 Mosler MT900 2003–2004 Holden Special Vehicles Clubsport SE (Y Series) 2003–2004 Holden Special Vehicles Coupé LE (Y Series) 2003–2004 Holden Special Vehicles Coupé4 AWD (Y Series) 2003–2004 Holden Special Vehicles Avalanche XUV (Y Series) 2003–2004 Holden Special Vehicles Avalanche XUV AWD (Y Series) 2004 Pontiac GTO 2006–present Elfin MS8 Streamliner 2006–present Elfin MS8 Clubman

References:

https://en.wikipedia.org/wiki/General_Motors_LS-based_small-block_engine#3.89...

Reason:
Can you find one online that looks exactly like these though? any rods I find online that fit the mentioned vehicles do not LOOK like these.

Those appear to be Gen III LS 4.8 rods and pistons.

References:

https://www.ebay.com/itm/113753081209?chn=ps&norover=1&mkevt=1&mkrid=711-1171...