What are your conserns about this rifle? I see the upside down stamping, that is odd but, I think it's a factory mistake.

I have one very much like it #490.

Frank

what, pray tell, is a "firing ring" on the lever? is this some arcane gun-broker auction house speak?  If so it left off "unusual" and "rare"

Very interesting.
Good observation!
I know at Winchester ,we used a rolling dies to impress the writing on barrels and receivers.
You can see the impressions on this rifle are not hand done.
Must have been different dies for each line.
We would have scrapped a mistake like that at USRAC, and the workmanship back when this rifle was made was supposedly better.
Perhaps an employee took this home and made his own from "borrowed" parts.
This supposition might also explain the stock bolt.

I don't think Ballard would have scrapped a receiver over that

Well, we'll never know for sure, but it's very hokey.
The "firing ring" on the lever has a hole in it where it meets the receiver.
Is that common? If not, this might also speak of it's non-factory origin.

Rebel, in the serial # range of that rifle, it is totally straight.

It's a very early Marlin Ballard, and thus has several features found on Brown Mfg. Ballards, as John Marlin started out assembling Ballards from leftover Brown parts. 
The lever with a "return" on the end is early, as is the locating pin for that lever. Some early Marlin Ballards have both; while some have the lever (with or without hole) and some have the lever, but no pin in the frame. Some even have the hole in the frame for a pin, but no pin installed. 
The #1 Ballard all had round top receivers, and round barrels. The #1 1/2 had round barrels also, but octagon top receivers, and unlike the #1 which was cast; all #1 1/2 are forged receivers.

The gun at auction is a #2, and also has the early style hammer and trigger, which were Brown items too. It has the deep crescent buttplate, but as Frank mentioned, the stock bolt is under the plate. My earliest Ballard is a #4 Perfection in serial #48x, and has the stock bolt under the buttplate.
Often Marlin mixed the spare parts they got when they started production, so there's no cutoff date for certain things. I've seen much later guns have early Brown parts on them. If they found a box of parts, they simply used them up, without wanting to waste any usable parts. Which explains why the upside down stamped receiver got used also.

Frank, I've never seen a pin in the frame that was "threaded"! All that I've observed were smooth. I'd like to see yours on your Ballard. Wonder if the threaded pin is original, or something added later?

PS-The seller mentions the changeover from JM Marlin to Marlin Firearms Co. as 1876-1880, which is incorrect. JM Marlin was the company John Marlin started in 1870 to build handguns, and the change didn't happen until 1881 when he began making lever action repeaters. He incorporated at that point, and the company name changed to Marlin Firearms Co.

Vall,
Your right as usual Not sure why I thought it was threaded but, I even had a mental picture of it. Here is the "real" picture And a better picture of my butt plate.

Frank