Dear Lee
Your solution for that is a good approach. In that way the original harness remains unaltered, and you have the possibility of fitting the right type of clock in place in the future.
Use as you mention a male 4 plug connector to fit your existing female 4 prong connector on cars original harness, from that interphase make a cable extension that connects to new clock via spade female terminals, providing the positive signals. Ground via a “0” type connector to one of the fixing screws.
Best regards
L.peterssen
Ps I have seen on eBay some reproduction clocks for pagoda listed at usd 125, no5 so expensive as the original.