I guess I can speak for New England a bit more:
Boston and Maine initially dieselized freight, or some of it anyway with FT’s in 1943-44, and E-7’s for some passenger, especially the Boston-Portland (Me.) service.
The FT’'s lasted only 12 years, and were traded in for GP-9’s.
In 1954, they began to convert all of their passenger services to RDC’s.I think that thry were done with this in 1956., and I am going to,leap at a guess of 264 of these cars from lonfg=ago reading.of Bob Willohby Jones’ books.
If RDC’s jhad been availab le in the 1947–50 period, I would imagine that They would have started dieselization with them…so, did they dieselize with RDC’s? Well, not technically, but maybe practically.
But the B&M put their FT to work on passenger trains also, first by have a few steam generator cars, and then by installing boilers in the B units, which had space for them. In passenger service they generally ran with and A and B. In freight service they started out as A-B-B-A, but quicly moved to an A-B-A or A-B-B formation for their heaviest trains. This in some cases involved replacing drawbars with couplers.
The B&M used a lot of GP-7’s and Alco RS-2’s and/or RS-3’s with boilers and head end lighting power in Boston suburban passenger service until the RDC’s took over completely. The GP-7’s were in the 1600 series and the slightly earlier Alco’s in the 1500 series.
I rode 1567 and 1568 many times in connection with my MIT SB-EE thesis. Ran a freight once too.