NHTX: Thank you, that was what I need to know. I was concerned the round roof hatches on the Athearn model would be a dead giveaway that the car was later than 1954. I will look for that book.
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-Kevin
Living the dream.
The major spotting features of the 2600 cf Airslide covered hoppers built between January 1954 up until 1955 are squared vibrator mount brackets and open bottoms on the side stakes between the channels on the sides. The triangular gussets are a change made in 1965. Athearn's 2600 without the gussets and with the squared vibrator brackets is very close to what you are looking for because whether or not the bottoms of the side stakes are open is not apparent at common layout viewing distances and, is just a beautiful car. If you can locate a copy of "A History of the General American Airslide and Other Covered Hopper Cars" by Eric A. Neubauer as Freight Cars Journal Monograph No. 9. This book gives you all you may ever want to know about these cars. In addition to spotting differences, drawings, and photographs, it also contains very detailed rosters for all of the different cubic capacity cars, including in many cases lessors by car number. Unfortunately the book was published in 1989 and may be hard to find. The ISSN is 0884-027X.
Concor site says 2600 cu ft airslides built built 1953-69
https://www.con-cor.com/website/product/ho-2600-cu-ft-airslide-covered-hopper-r-t-r-pennsy-1960-01-97070/
I found a site that said the triangular gussets were added to the design in 1965 making the cars without gussets the earlier design. Confirmed by looking at dates in photos of the prototype.
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
Burlington hopper has a build date of of 4-65. I can't read the build date on the second car, but I believe they are both built by Athearn using their new tooling with the delicate ladders and grabs. Most Athearn cars in this series have mid to late 60's build dates. They are really nice RTR cars. I have several. I can't find a current 2600 Airslide hopper offered by anyone other than Athearn. Con Cor marketed one in kit form years ago, but it had the heavy ladders of the era.
This appears to be early car
http://www.historicrail.com/GATC-2600-Airslide-Hopper-HO-Scale/productinfo/400748/
Athearn car appears to be slightly later design
http://www.athearn.com/Products/Default.aspx?ProdID=ATH87507
edit. Based on additional information the car without the triangular gussets on the ends is the earlier design. So I got it backwards.
What are the spotting features of the first airslide hopper cars made in 1954? If I get one of these it needs to be the very earliest example made.
Is the Athearn car even close?