I don't think you want to sign a return saying that the numbers on the return are only guesses.  What records are unavailable that can't be generated or rebuilt before the extended due date?

I agree, thank you.   I was only wondering if IRS had any specific procedure to allow a temporary estimated filing until reconstruction of records could be accomplished.  The deadlines have expired on two years.  Taxpayer in Assisted Living facility, but now working with the POA son to reconstruct records.  Fortunately, I believe ES's covering most of liabilities have been paid on overdue years. 

Thanks again.........  

You betcha!

Wage and income statement will generally identify the income received. I use W&I as a basis when source documents are not available. 

Thanks Skylane.

That will work for some of the items and I will do that, but our big unknown is some residential rental properties that we'll have to reconstruct from various sources.  Thanks for the input!