School me on the pros and cons of a normal 6 counterweight crank vs an 8 “full counterweight” crank for a typical BBC bracket engine. Weight differences? Performance considerations? Longevity?

I can't speak to performance. I have never seen anyone spend the money to do a ABA test. There is unlikely to be any HP gain there. It's just not logical.

I will say that from a longevity, main bearing wear and balance standpoint a full weighted cw crank wins going away.

Weight, since you are bracket racing it makes no difference but you can spend more money getting a lightened version....but then it likely gets flexier. You have to balance potentially improved acceleration vs longevity.

Crower 6 counter to Bryant 8 counter. 11hp gain with the 8 counter and it's 3.5 pounds heavier. Everything else the same.