7 1/4 Can handle how much

i have a slant six with a 4 speed 9 to 1 with a mild camshaft 473 lift 255 duration super six carb 2.5 exhaust after breaking in the new camshaft less than a week BANG busted one gear off the ring gear. I had 3.55 in that rear my question is do I just need to upgrade to a 8 3/4 or was I just unlucky this time? I doubt I have more than 150 hp and the wheel. What do you guys think I had a 4 speed with a v8 and a 7 1/4 never had any problems dumped the clutch all day.