I picked up an LN3 and Im not sure if it runs do I need the computer to get it to run?

You mean to get it to run in a CAR? YOUR car? Something else?

More details would help.

I mean just to play with it in my garage.

You need a fuel tank, a battery, and a PCM. You'll also probably have to trick VATS.

Just to play with in it the garage? Is this going on a go-kart?

the 88-91 bonneville with the LN3 didnt get VATS so if he gets an ecm from one of them it the vats wont be required.

Ventelation, good ventelation And some ear plugs if your going to do open headers

GO KART!

you gonna rebuild it? or...

Yep, you will need a type 253 ECM to read the sensors and drive the fuel injectors (Service #01228253). The rest of the ignition is pretty much self contained in the Ignition Module under the coil packs.

I'd love to see what you are going to use as a test stand for it, or are you just going to plunk the engine/transaxle/cradle assembly down on the floor ?

Either way, you'll need a high pressure fuel supply and return line from the injector rail, and a cooling system to run it for any length of time. You can loop the PS pump lines back to the resevoir if you don't have steering rack. You can also loop the transmission cooler lines back as well. Plug all your loose vac hoses and light it up.

Gone are the days where you can just pour a little fuel into the carb, spark the starter, and watch the motor flop around on the floor like a toy top.