I found this article:

http://articles.latimes.com/1992-05-13/news/mn-1663_1_hoover-crip-gang-member

It's mainly a general article about ETG and their collective 'rap sheet', but it does mention their beef with the Rollin' 60's and the fact that they (the 60's) robbed an NG armory in the 70's. Doesn't give any specifics about the robbery itself, however.

I'm going to do some more article digging on google since I'm at work and awaiting assignment, but I doubt I'll find much. I'll be at my old school friday (auditing a class for shits and giggles) so I'll give the newspaper archives a perusal while I'm there. If this actually happened and isn't just gang folklore, I should be able to find some media coverage of the event from the time.