Based on some limited caption information in Gerald Best's 1961 article in the R&LHS Bulletin about the steel cars, they appear to have been fabricated in the IRCA Guatemala City and San Salvador shops using the trucks from retired wooden cars. Since there are pictures of trains with all wooden cars as late as 1952, apparently the steel cars date from some time in the 50's.
I browsed through my IRCA annual reports (I have a more or less complete set from 1912) the only mention I can find of what is most likely the wooden cars is that they are "imported". But whether they were new or used is not mentioned, at least based on a quick perusal of the annual reports.
But the wooden cars do look much like DRGW cars. If I remember correctly, the wheel diameter is smaller than the DRGW standard, and the coupler heighth is lower. But other than that.....they would look nice on the C&TS.
JBW