The round inlet is 25mm (1 inch) diameter, measured with a scale.

The outlet is 42mm (1-5/8 inch) horizontal by 32mm (1-1/4 inch). vertical.

The transition distance is 70mm (2-3/4 inch) face-to-face.

If you use the Westlake-style adapter this won't make any diference, of course.

FWIW,
Charlie