Jim & Earl
Regarding folio and similar measurements: The D&RGW locomotive diagrams issued in the 1950's, and formerly available from the Maxwell Collection, do indeed show boiler barrel "OD"s. This is a contrast with the industry's standard, which is to give the inside diameter of the front sheet. So Earl's additional 3-4+ for lagging should be added to a model boiler. And misinterpretation of such dimensions is doubtless why some models come up so short on visual boiler diameter.
For the K-28s we have much more much more specific information, from a seven page ALCo publicity piece in the Railway Review of January 24, 1925, V 76, No 4, pp 179-185. This was also formerly available from the Maxwell Collection, but I believe it is now online, possibly as the 'Railway & Engineering Review". The table of dimensions and quite detailed drawing both give the following:
Diam, smoke box 65 3/4"
Diam, first course, outside 63 1/2"
Dim, second course, outside 66 1/16"
However such sources rarely if ever give any details about the lagging, so I cannot improve on Earl's dimensions.
This ALCo publicity piece is an unusually detailed exposition of a locomotive's design goals, the means by which they were achieved, and the operating results. It is essentially a demonstration of the advantages to be expected from modern 'super powered' steam, although the ALCo publicist never even hints of that phrase. The K-28 was a thoroughly modernized K-27, incorporating all applicable elements of the intervening 20 years' improvements in steam locomotive design. In the K-28, the D&RGW obtained an engine that could take a K-27's load wherever a K-27 could go, while making remarkable savings in fuel, water and time over the road. Regarding NG operations in 1924, the ALCo publicist reports that "For the first six months of this year ton miles per locomotive mile have increased 13 per cent; freight train speed has increased 22 per cent and gross tone miles per train hour have increased 35 percent." Much of the improvements was doubtless due to the increased number of heavy NG freight engines, from 15 to 25, but it was clearly the K-28s' performance in freight service that justified upgrading the principal NG lines with rail and bridges heavy enough to allow introduction of the K-36 and K-37 classes.