Re the modified Chipmunks. I presume they were all Experimental. Do you know if proper stress-analyses were done or did they just cut bits off, add bits as required, bolt-on a new engine and go flying?
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!
After 50 years, there is no way to know what analyses were done by the guys modifying the Chipmunks in Experimental category. Government oversight has no bearing on the level of analysis that may have been done - there are lots of good designers and analysts available, and lots of smart aircraft owners. Its called land of the free and home of the brave for a reason, and we like it that way.