Find the oldest known descendant of the Individual you are searching and do their DNA test on Ancestry. Once you have that result download the raw DNA from Ancestry and upload it to FTDNA, MyHeritage and Gedmatch. Ancestry does not allow uploads from other companies, so if you test at any of the other companies you cannot upload to Ancestry to compare matches at that site. Uploading Ancestry results to these other companies allows you to find shared matches on any of those platforms, not just on Ancestry.

If you are absolutely sure you have a male descendant (son of a son of the 1917 unnamed father) then do the Y DNA test. It has to be done on FTDNA. In this case it might be cheaper and more convenient to do the Y and the autosomal on FTDNA, but you would then be missing the matches on Ancestry. Unless you have 2 descendants you can test - one for the Y+ autosomal and one for the autosomal alone. the more DNA you have from known descendants the more information you have to work with.

I have done this successfully using my uncles Y (son of a son of a son) and others peoples autosomal DNA and recently we found the biological father of someone who was a DNA match to our family, and has been searching for his father all his life. To everyones delight and joy.
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Cathy Miller, New Zealand
cathymillernz@...