There is a listing for your Idwal Owen on the RootsWeb WorldConnect
http://worldconnect.rootsweb.com/cgi-bin/igm.cgi?op=GET&db=menice&id=I319. You might try e-mailing the address listed under "Contact" as that person may be able to provide you with more information.
With that info, I was able to find Idwal on the 1920 US Census in the village of Fair Haven, Rutland County, Vermont. The family, living at 14 Capital Hill, has info as follows:
David A. Owens, head, age 54, immigrated 1899, naturalized 1911?, parents & self born in Wales, superintendant of slate quarry
Mary E., wife, age 41, immigrated 1892, naturalized 1911, parents & self born in Wales
Edwal A., son, age 5, born in Vermont
Jane Davis, mother-in-law, age 78, immigrated 1892, alien, parents & self born in Wales
Also, I noticed, listed on same page, different street (couldn't decipher street name):
John Owen, head, age 32, immigrated 1913, filed first papers to become citizen in 1915, parents & self born in Wales, minister at Welsh? church
Annie, wife, age 39, alien [due to marrying an alien], born in Vermont, parents born in Wales
I don't have access to an index for the 1930 US Census, but I have found David Owen(s) on earlier censuses, if you're interested, let me know, and I'll forward the details.