Just looked at the 59 CR report and see the 66 would have set you back $109.95 but the 31 was only $69.95- think that may explain why the 31 seems to be a lot more common!.
At this time I believe there were about $3 to the £- The 1334 Junior was about £28-29 and the 652 Senior was about £10 more, although I think the Senior came with the tools.
It makes you realise how much of an investment a Hoover would have been then- in the case of the UK the Senior would have set you back nearly 3 weeks good wages!!