Firstly, I don't know this exact model of pump, but you could get a flange fitting made up for far less then $800 in any toolshop. Hi-vac stuff will have a SS flange with a replaceable copper gasket or such - this is excessive for typical requirements.
Most lab. stuff needs very moderate pumping speed - 9mm bore tubing - so it's not as if you need high throughput flexible SS assemblies.
The interstage will probably give sub-millibar pressure so is good enough for normal lab work. Shame to ignore the main pumping port though,