what is the difference between internal and external balance? which one is better? what do i need to know about this before i start building my motor.

externally balance is done by the flywheel and harmonic balancer weighting. if it's a 350 you are building it is probably internal as most are. i think 400sbc's are mostly external...ie you could use same balancer on a 305,350 but not on a 400

so the 1989 L98 that i took apart is exteranlly. even though im gonna stroke it?

The L98 you took apart is internally balanced - the harmonic damper is "neutral" balanced. The weight on the flexplate/flywheel is only there to take the place of the counterweight that used to be part of the crank on two-piece rear main seal engines (including 400's) outside of the rear main bearing. All '86-up SBC's are one piece rear main seal, internally balanced, and require a weight on the flexplate/flywheel. All 350 & smaller SBC's use a neutral-balance damper.

The factory 400's were externally balanced because there wasn't enough room inside the crankcase to properly balance the longer 3.75" stroke without using expensive, high-density metal in the counterweights.

Whether you will have an internally or externally balanced 383 depends entirely on the crankshaft you get. Many one-piece rear main seal 3.75" stroke cranks are now internal balance - you need to specify when you choose.

thanks for clearing that up with me. i was confused about that for a lil while.