[cprflash]

I have a 350 sb I'm putting together and it came with the 8" harmonic balancer but a lot of the rubber in the ring is missing and cracking. Is this fine? I also have a 6" harmonic balancer from a 305. If the 350 one is not good enough, could I use the 305 or were they balanced different? Thank you.

[bigdog7373]

You should replace it. If it's an internal balance engine (which i believe it is) you can use any internal balance balancer. For external balance you must use a 305 external balance, but i believe all 305s were internal balance

[DoubleVision]

Replace the balancer with a new 8 inch unit. All generation 1 sbc's were internal balance except the 400, which was external balanced which is why balancer and flexplates should not be interchanged between the two.
While you could use the balancer off the 305 the timing marks won't line up just as well as the 8 inch balancer does a better job.