>Also, I have heard the locomotives maybe coming out of Columbia, and resemble a modern (more modern?) GE 70 Tonner.
One might say that the GE 50 ton export model (SP #1, SVRR #720) was a scaled down version of the stock GE 70 ton but with a Caterpillar vs. Cooper-Bessemer engine. This was apparently at the instigation of the original buyer United Fruit Company, and appears to have been a competitive bid against an earlier design they bought from Whitcomb (which used a Cooper-Bessemer engine). The Caterpillar D-397 engine was fairly new on the market at this time. The 50/52 ton sold fairly well to Central America/Caribbean and the Philippines.
Most think that GE's domestic U25B was the beginning of GE's Universal series, but it was actually earlier than that in 1956 when GE announced a standard "Universal" line of locomotives. Some of the larger ones were for standard gage or wider, only the U18BD was aimed at the North American market (Mexico bought a few), all the rest where for worldwide use. The two smallest models were end cabs with Cat engines (replacements for the 50/52/70 ton lines), while the larger models U9B/C through U18 series had 6/8/12 cylinder Cooper-Bessemer engines.
GE's Caterpillar powered U series and their variations were built into the 1980s for various customers in North, Central and South America, Spain, Greece, Philippines, South Africa and a few others scattered around. Perhaps the first ones of the updated model built were the USG 54 tons now at the Loop, though they were never designated as such and more likely a modified model to meet USG's requirements. Some model designations such as U6B, U18B and UM10B were reused over the years, and represent various actual designs.
There are still quite a few in service around the world, but they are getting up there in years. A bunch of U8B went to Vietnam during the war, some are still running and have been upgraded with newer Cat engines.
