The only L-5s redesignated U-19A were the very few which were still in service in 1962. The rest remained as L-5s because they were either in museums or in the hands of civilian owners.
I'd use the c/n for profiles unless the c/n is unknown. If the aircraft has operated with s/n and c/r, or was c/r and now in museums with c/r cancelled, I'd link them because that way if you didn't know the c/r or s/n you could search either one. Otherwise, if the plane is c/r, perhaps the s/n could be in comments rather than another profile. Just an idea.
42-98225 can remain linked with N66225, since they are the same aircraft. I would not mention the bogus markings except in a comment -- not in the ID section.
42-98271 should be linked with N49279
42-98667 is c/n 76-908, but FAA uses the military s/n as ID (as filed by the owner). Since this is registered by the s/n being the c/n this adds confusion for searching. Possibly show c/n as the s/n and comment with the c/n?
42-98239 is c/n 76-480. Same problem as with 42-98667.
Glenn