for posting that link to the combination article. It was quite interesting.
Here is another site you might try to search for a replacement tank and required fittings.
In the restoration of my '65 I intend to consider providing a combination holding tank ... when & if I get back that far ... I started in the front and am slooowly
my way to the rear!
PS. There are also some shower pans available on this site for those of you that have to create a new bath.