Hi Luke - I fully understand the desire to keep the original keyswitch to preserve the c5 as it was manufactured , but the reason the c5alive wiring kit was introduced about 10years ago was to deal with the reliability snags caused by failing keyswitch assemblies.
Those same keyswitch assemblies are not going to be getting any more reliable as they age, so hate to say it - your dad is right a c5alive kit is the way to go
I hope to
bully ask RadioMarty nicely if he is up for helping to make another batch once Christmas is out of the way.