Hmmm, another thread with pictures from 10 years ago of a 403. It's like Deja vu, all over again. •》jmo, 403s and high rpms don't go well together. 5,500 rpms should be the top of your limit. When it goes, it really goes. I've seen lots of 425/455 let go also.
General Discussion - OUCH 403 Goes Bye bye - I'm a fan of the 403s but stuff does happen. Owner does a good job of explaining and picture taking. Imo. https://www.tapatalk.com/groups/realoldspower/anyone-ever-use-jb-weld-t16955.html
Martin was a teenager when the original Olds Power existed and an active member. His 10 to 1 403 was putting out serious power. Add a T-56 and a flimsy 403 crank this is the result. My 7.5" rear exploded in a similar fashion and situation.