Hi Dave
It also worrys me that you may be going down the wrong track.
On the 1901 Census he is recorded as William R Clucas b.1862, Castletown whereas Richard Wiliam Clucas (Pugh) was actually born in 1864 - that said dates of birth are often not accurate on Census records.
Is his name William Richard or Richard William on Mona's birth certificate?
For information there was a William Clucas baptized at Malew Parish Church on 8th June 1862, mother Eleanor but I can't find any trace for either of them in the Census records.
Derek