Depreciation Basis for Condo Bought With Vacant Land 1031

[John Haelig]

We purchased vacant land in the 1970's for $70,000.  Sold it in 2018 for $720,000 and 1031 exchanged for 3 condos now used as rentals.

Since the sold property was vacant and never depreciated - what is the cost basis and depreciation schedule for the new condos?

Should it be as in a new purchase i.e. dwelling deprecated over 27.5 years?

Or - some formula based on the vacant land purchase & sale prices?

What is entailed in "opting out" using IRS Form 4562?  Would that come into play here?  

My only understanding of that is from a memo I found on line written by Realty Exchange Corporation. 

Many, MANY thanks