Just to show Mr. O'Connor that there is more than one person capable of answering that question, I logged 200 cars of the R-30/40-19 class from the PFE Rebuild List to get a sample.  What I found is that the thousands of cars in the R-30-2-13 class have been overlooked - and is an error in my chart that Bruce Smith referenced.  

Of the 200 R-30/40-19 cars that I logged, 58 cars (29%) were from the R-30-2-13 class, 93 cars (46.5%) from the R-30-12 class, 24 cars (12%) from the R-30-13 class, and 25 cars (12.5%) were from the built-new R-40-2 class.  So for that sample of cars, the Bettendorf underframes were less than half of the class.

I have no expectation that this data is necessarily the same for other rebuild classes.  In fact, while I have not checked the listings, I have never seen a photo of an R-30/40-24 class car with a Bettendorf underframe.

The PFE Rebuild List and also the individual Car Cards are available for research at the CSRM Library in Sacramento, CA, or copies can be purchased for research elsewhere.

As Tony mentioned, all the brake rigging, and most of the piping, is below the center I-beam of the Bettendorf underframe - an obvious spotting feature in photos.  The only hole in that I-beam is for the crossover of the trainline brake pipe.

Bob Probst was another guy capable of such answers, but unfortunately he is no longer with us.

Maybe by the time I give my next clinic at Naperville - modeling PFE wood ice reefers - I'll have even more data about underframe proportions in the various classes.

Hope this helps,

Dick Harley

Laguna Beach,  CA