Presuming you have a 5 speed Lumina Z34, than you have a Getrag 284, unless it's been swapped.
Order axles for 91-93 Lumina Z34 with manual trans and you'll get the right ones.
Tip, ensure the stub shaft on the driver's side axle either stays in the trans, or you remove it from the axle BEFORE you hand it in as a core. You'll be searching for a new one and won't find it easily!