KC,
Welcome to the forum!
Marty has some excellent FAQ's on this site for finding files etc. For me; the easiest has been just to look on the TIGHAR home website's "Site-Map" and scroll down it.
I have attached a pdf (of 164 pages) which is a copy of the FAA's file on the Electra in question. This is a public document and you can order one (for any US Reg. AC) from OKC on a CD with the exact same pdf for $10 including shipping. Takes a month or so (they have to photograph each microfiche page back/front and burn the CD) and has no better resolution than the online version. I downloaded this one from AvWeb (I think) and don't know if TIGHAR has a copy for download on site.
In addition to all the certification records, it contains what we now refer to as "337's", scroll down to page 59-71 to see what was submitted by Lockheed to the FAA (CAB back then) for the airframe repairs after the ground loop. I have no idea what the policy was for 1937, but the FAA has gone back and forth on the requirements for submitting "Engineering Drawings" for repairs.
I would check Perdue's Archives for possible Maintenance Log copies, they should exist.
As far as rivet patterns, I'm sure you know from your background but for the benefit of some other readers: No two aircraft will ever have the exact same rivet locations, when you replace a section of skin or airframe, you start with a blank (as far as holes are concerned) and must drill each rivet hole to exactly match the existing corresponding hole from where the old panel was removed.
There has been a lot of forum discussion on metallurgy testing for found aluminum, on the site-map you will see many years of archived 'email-forums' by the month, no 'threads' or 'topics', you just have to do a Key-Word Find to read a specific topic within a month. If you just want to read the whole archive, I found it best to copy/paste each month from the Browser into MS Word, where you can easily control the view, layout, font and format as well as save anything you want to keep.
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Well all the excitement must be overloading the TIGHAR Servers as I have tried five times to post this (with the attachment) and it just creeps up to 100% in three minutes and then kicks me back. Here is a download link:
http://www.planefaxreports.com/pfr/pdf/n16020/16020-Registration.pdf