If a balancer/damper separates or breaks in half ... the motor will vibrate heavily and things will begin to crack/break. There's a lotta opinions whether one should use the stock elastomer-type damper/balancer or a big-$ fluid-filled type. GM uses 8" elastomer balancers on even their hot crate motors. A leading manufacturer of hi-po stroker crankshafts (SCAT) also recommends an elastomer balancer. Sure the rubber can fail and the outer ring can slip ... but usually only after many years of attack by heat & oils ... & trying to remove one by prying on the outer ring will accelerate the process. Many vette sbc came with the 8" elastomer damper. Far as I know, sbc 400 came with 8" external-balance damper. IMHO, if an 8" balancer will fit, most street sbc's will do fine with an 8" elastomer (aka rubber) balancer.
JACK:gap