Dave,
It does look as if the dial face is perhaps held in position by the “madnolia” bezel. If so, we’re that bezel removed, a couple of spots of superglue or hot glue would probably serve a similar purpose.
Having had my attention caught – but finding myself unable to answer the subsequent question – I dug out and measured an old 4-cyl rad and water pump. I can confirm both hose connections are 40mm.
Happy drilling and tapping.
B…..
Bernie