Are 4.3's internally or externally balanced?
 

Title says it all.I can't figure it out

Balanced how? They have a internal counter balance shaft for the cam. At least my 2002 & 2004 engines do.

I'm doin a 4.3 swap in a Toyota truck and I need to run a 153 tooth flywheel.they sell internally and externally balanced flywheels.so I guess is the crank shaft balanced?I believe the motor I have is a 95.its got the big intake manifold.

4.3 balance shaft
 

Has been used since 1992 and up.The engine had an internal balance problem because of the 90* block design and the way it fires.Its either odd fire or even fire cant remember exactly.The balance shaft was to cure the internal vibration.
The crankshaft in externaly balanced hince harmonic balancer on the front.The flywheel is also balanced.
Hope this helps.