Grand Falls Central 101-103, GE serial numbers 33257-33259, built January 1958.
"Diesel Era" magazine had a two-part article on the 70-tonner, in issues v.4/n.6 (Nov-Dec 1993) and v.5/n.2 (Mar-Apr 1994). The first part has a photo of one of these units and a brief discussion: they were "Phase III" 70-tonners, the final variant (with recessed headlights and simplified sheet-metal work on the hood), which was not bought by any U.S. customer. They were "active until sold to Nicaragua in the late 1980s."
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As for whether they were "ideal" for the application… Both the GFC and CN's PEI lines were axle-load constrained (note that when CN put locomotives with 12-cylinder Alco engines to work on PEI, they equipped them with A1A trucks to spread the weight). So probably nothing much heavier than a 70-tonner would have been acceptable. GFC got three units, with m.u. capability, suggesting that MAYBE they could have used a bit more power, but probably the 70-tonner was a good fit to their needs.
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Other GE 70-tonners built for Canadian customers (going by rosters in "R&R" article): British Columbia Hydro 940-943 (GE #30371-30373 and 30386) of January 1949, Canadian National 7802-7819 (GE # 30608-30625) of March-May 1950, Pacific Great Eastern 552-557 (GE # 30037-30038, 30177-30178, 30440-30441) of March 1949, June 1949 and February 1950, Spruce Falls Power and Paper 106-107 (GE #30387,32306) of Feb 1950 and June 1955, and Thurso & Nation Valley (I think that's in Canada!) 5 and 7 (GE # 28238, 30179) of Oct 194 and July 1949.