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."
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.
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.