Talking O-27 conversion - I'd wondered about the K-line semi-scale offerings and came across this.
The old Atlas O "Industrial Rail" 4-4-2 from what I've read is 1:64 or darn close to it. Even a "scaler" or two have converted one.
As far as the K-Line ex-Marx freight cars go, they are more or less 1:64. IMO they fall into "eye of the beholder" territory. I had considered trying to covert some to scale, but I found the detail too crude (cruder than the Lionel "Scout" boxcar) to make the effort.
K-Line was going to produce some freight sets using a modified ex-Marx 333 Pacific, but K-Line went under before that could happen. They would have been interesting.
Several S-Fest cars were produced using the K-Line cars.