The Aircraft Design And Certification modification is applicable in
Canada (I'm surprised that it's not approved in the U.S. yet as
usually a method approved by the agency which controls the original
type approval for compliance with an A.D. issued by the same agency is
accepted by other governments as a matter of course) but so far as I
have been able to determine no one has had it done. Possibly if you
had an L-13 with no more than 2000 hours and which was otherwise in
very good shape and well equipped it might be worth doing. In Canada
the factory life limits and life limit extensions were applied as an
A.D. so my club sold it's last two L-13's several years ago for around
$4000 with trailers when they reached 4250 hours. At that point it
seemed that the cost and work involved in pursuing one last extension
wasn't really worth it. It hurt to sell them but we had been
depreciating them based on zero residual value at 3750 hours so at
least we were ready for it.