Engine type restrictions were listed in the Time Table in Rule 1710 (according to the April 29, 1951 issue).
For PA-1s and DL-109s any restrictions would have been on lightly-used branches with no passenger service. Also, any restrictions would be due to the engine's weight, not its length or wheelbase. A DL-109 could handle a curve as severe as 21° (274.37 ft or 83.63 m).
New Haven/Hartford Division restrictions were as follows:
Branchville and Ridgefield - DERS-3
Canaan and Lakeville - DERS-3
Highland Jct. and Watertown - DERS-3
Vernon-Ellington and Rockville - DERS-3
Farmington and New Hartford - DERS-3
Northampton and Williamsburgh - DERS-3
Boston/Providence Division restrictions were as follows:
Providence and Bristol - DER-2
Westdale and East Bridgewater - DERS-3
Tremont and Fairhaven - DERS-3
New Bedford and Watuppa - DERS-3
Franklin Jct. and Hopkinton - DERS-3
Note - The DERS-3 was the Raymond Loewy-styled FM H-16-44 (0790 series). The DER-2 was the Alco FA-1 (0400 series).