Owl Mountain Models produces HO scale brass castings for these vents. Scroll down on their Detail Parts page to see them

http://www.owlmtmodels.com/detail_parts/detail_parts.html

Eric Hansmann
Murfreesboro, TN

Colin,

You don't specify era and that can be important. Typically, the guidelines seem to have gotten a bit easier over the years.  Working from the 1934 version of the ARA Rules Governing the Loading of Open Top Cars" The Insley Excavator qulifies as a "machine on which body portion rotates". The following generalities seem to be generally true.

The boom should be stored in the lowest possible position. In the case of the Insley, this would either be fully extended or fully folded (I'd sugges that latter).

Tracked vehicles are secured by means of angled chocks at each end of each tread to prevent forward and back movement and guide boards (2x6) nailed to the deck alongside the tracks, either outside or inside the tracks, to prevent lateral motion.

The rotating body is supported by a wood frame at the back end

The rear of the body and the boom are secured to the side of the car with wire or chains to prevent rotation

Any portion of the boom assembly that might contact the deck are shimmed up with wood and may also have bracing to prevent lateral movement. 

Parts of booms on different sides of joints that come into close proximity may have wood blocks inserted to prevent contact between sections.

Regards,

Bruce

Bruce Smith

Auburn, AL