How did Jumbo Tsuruta die?
I never found that out.
I read some interview with, I think, Johnny Ace where he talks about it vaguely and makes it sound like he died in the ring. What happened?
Jumbo Tsuruta most certainly did not die in the ring. Tsuruta announced his retirement on February 20th, 1999, due to failing health which was contributed significantly by Hepatitis B, which he contacted in the early 90s. He died on May 13th, 2000 after a failed kidney transplant.