I ask this after having read the horrifying report on the Galloping Ghost P-51 crash at Reno, where major airframe changes were made without any stress or airworthiness analyses and without approvals!
I believe that there is an STC for the Lycoming engine on a Chipmunk. In which case, it's airworthiness would be documented.
Yes, the P-51 crash is an indicator of some things missed. Though I will be railed by those who love the air races, I don't agree that aircraft are flown "in public" at speeds they have never before achieved. For certified aircraft it is required that a dive test to 110% Vne be flown - I did one just the other day. Thus pilots who blunder up to Vne can be confident that they're not charting new territory (though they sure are close). I believe that the fatal chain of events with that P-51 was speeds in the "never before flown" range, coupled with inadequate assembly/maintenance on the elevator trim tab. These things should all be worked out in a safe "test" environment, before these aircraft are raced in front of the public.
The general public would have a hard time understanding the subtle differences between "Experimental", "Amateur Built" and "Certified". So crash one and kill some innocent observers, and the public will brand all similar sized aircraft as unsafe.