1962 Plymouth Valiant

Hi all, have my '62 Plymouth Valiant here in Australia and want to upgrade to a 'dual' Brake Master Cylinder. Have found a Willwood MC kit #WIL26113269 which I can buy, but it needs an adaptor plate between it and the firewall. Any of you guys know where I can get one that will fit my firewall?

There are adaptor plates available here in Australia but they are mainly for the later Chrysler Valiants, so I have been told.

cheers in advance, col.