Same answer as for the United States: Multi-member national house election by a competent method of single transferable vote (although Meek's method is newer than that, and my Bucklin-based method isn't even fully analyzed yet, so only somewhat-competent methods existed); single-winner elections by a single transferable vote nominating primary followed by a Smith-efficient final election (although the Smith set wasn't defined until later; Condorcet paradox was known, and inventing the Smith set wasn't hard, modern methods which would allow for rapid hand-counting were only invented a couple decades ago though).
Easy problem today, harder problem at the time due to lack of knowledge.
They used a list proportional system (the same system used today in Germany, and similar to that used across Europe). Candidates were controlled by the party, rather than self-nominated. It's a huge oligarchical system that lends itself to enormous perversions of democracy. We have self-nominated candidates in the United States, but party primary elections and every type of election used here (MNTV, SNTV, first past the post, and run-offs) are broken and create extreme distortion, polarization, and disenfranchisement by their mathematical nature.
Democracy only works when it's actually democratic. When it's not, a polarized minority can become dominant over the majority, thus dominating the public discourse and shaping the public reason, retaining and expanding power. Most systems tend to reject whichever represents the view of the voters as a whole body; STV deals with the problems of fair and equal single-winner elections (which suppress minority voices) by proportionality for solid coalitions, capturing the median voter group as well as those minority views leaning away from the median voter in proportion to the size of the groups, which are of roughly-even size, thus introducing diversity into the conversation without lopsided a priori voting power, maximizing the efficiency of the public reason.
This is the "exception that disproves the rule" fallacy. It's like going back to 16th century America and finding the one black guy who isn't a slave, or the one white guy who is, and claiming that black slavery wasn't really a thing, just slavery itself as a general thing.
Easy problem today, harder problem at the time due to lack of knowledge.
They used a list proportional system (the same system used today in Germany, and similar to that used across Europe). Candidates were controlled by the party, rather than self-nominated. It's a huge oligarchical system that lends itself to enormous perversions of democracy. We have self-nominated candidates in the United States, but party primary elections and every type of election used here (MNTV, SNTV, first past the post, and run-offs) are broken and create extreme distortion, polarization, and disenfranchisement by their mathematical nature.
Democracy only works when it's actually democratic. When it's not, a polarized minority can become dominant over the majority, thus dominating the public discourse and shaping the public reason, retaining and expanding power. Most systems tend to reject whichever represents the view of the voters as a whole body; STV deals with the problems of fair and equal single-winner elections (which suppress minority voices) by proportionality for solid coalitions, capturing the median voter group as well as those minority views leaning away from the median voter in proportion to the size of the groups, which are of roughly-even size, thus introducing diversity into the conversation without lopsided a priori voting power, maximizing the efficiency of the public reason.