Here is a description of the process from the Gedmatch Wiki:

"The GEDmatch Lazarus process is so named because it can re-create the DNA of dead ancestors. It does so by combining the bits and pieces of matching segments from matches between you, your siblings, aunts and uncles, and close cousins. One example using 2 siblings and 3 aunts/uncles was able to achieve almost 100% restoration of a full SNP count of a parent. If close relatives are not available, it can also use more distant matches, but with less dramatic results.

It is not necessary to add data for every blank on the entry form, but more data usually produces better results.

The basic concept is that one group will be close descendants (son, daughter, or perhaps grandchild) and the other group would be siblings, cousins, aunts/uncles or parents of the target person for whom you want to recreate the DNA. Each kit can provide a piece of the DNA for the resulting target kit.

If a half-sibling is used, the half-sibling must be a child of the target parent."

I was able to reconstruct nearly 60% of my father's genome using me in group 1, and two first cousins and about 20 more distant relatives in group 2. (I'm fortunate that my paternal ancestors lived in a fairly contained rural part of Ireland so that I can pretty easily identify matches with ancestors from that region as paternal.) I then used that Lazarus kit to create phased paternal and maternal kits. Although there are significant gaps in coverage, that enables me to do a first-order approximation of which matches (other than those used in the Lazarus calculation) may be paternal and which maternal. I have another first cousing testing and will update the files when his results are in.

Blanche--if you are reading this, we are back to the Armagh McCann's. Although your mom and I have many shared matches from Cork, she matches my maternal phased kit, which has the McCann ancestors.

Jim