Well, taking a look at the CNW roster:
1940's and 50's passenger diesels are all in the low 5,000 series.
(all EMD except for the lone DL-109)
EMD FT freight units go up to the 5400 series..
Looks like either 5100 or 5500 series would make the most sense for late 40's Alco PA's..
(before or after the EMD FT's)