Bill – many thanks for the polite reply – not always the case on line!
David – fear not that your filter will restrict flow – as long as it is not heavily clogged. Smaller Gano filters than yours are fitted to some very high output american V8s and work correctly.

I pondered long and hard about the merits of the design before contacting the manufacturer; the idea of a blocked in-line filter is discomforting. But the alternative remains that the radiator core gets blocked instead, a rather harder thing to clean than the filter! Indeed sometimes back-flushing alone can’t solve the problem; recently looking at scrap cores samples at Star Engineering, particles combine with grease, oil and other gubbins to become aggregated into a solid mass. Horrid!
Certainly check the filter as regularly as possible at first; steadily the system will be cleaned and the device will need only occasional attention.