Isn’t there a nearly 10’ difference in wheelbase?
If I recall, the GP15-1 is just under 30’ and the F7 is 39’.
Unfortunately, a lot of sources out there confuse wheelbase (distance between the centers of the first and last axles of a loco) with truck centers. According to the drawings (C&EI) of F units, an F unit (and therefore a CF-7) has truck centers of 30' and wheelbase of 39'.
The "wiki" for the GP-15 (and I am sure several other websites and quite possibly some books) list the "wheelbase" as 29'9", but the loco length is 54'- a foot shorter than a GP-7 or -9. So, given that photos make clear that there is not 12' of overhang at each end, the 29'9" dimension is actually the truck centers, not the wheelbase. For comparison, a GP7 has truck centers of 31', and wheelbase of 40'.