So far as I can tell, These were initially intended for racing purposes from the start. I would bet by late 69, most in NHRA or World sponsored teams racing these found they did not withstand the extreme demands of all out racing. I think the last use of these were 70 to early 71 on a few select teams, & I couldn't even guess as to how many were used in the Marine racing circles. Who knows! Hard to guess when these fully caught on and probably difficult to obtain much after July of 69. Ironically, it can be seen that our Hobby has endured the long haul with respect and dignity due to the successes that the cast iron blocks provided us then as well as still today!
