Congrats on your retirement, Mike.  Now on to the usual factual corrections...

According to MOA property records, the building was constructed in 1957.  An Anchorage Press story from late 2014 refers to it as "A building constructed in the late 1950s".  I don't have easy access to Polk directories from the period, but the 1958 phone directory contains a listing for Lake Spenard Baptist Church at 3506 Spenard, whereas the 1956 directory contains no listing for that church.

The real devil in the details is in the property records.  Looks like the land is nearly as valuable as the building and there's no exemptions.  They would approximately halve their property tax burden by tearing it down.