The R.751 "Class 37" was fitted with two types of motor bogie.
The earlier (1967 - 1973(?)) is the "standard" Tri-ang 3 Pole "Open Frame" Motor bogie. The Later version is the "clip in" "Ringfield Motor" Bogie.
From my books, the earlier pattern looks to be a bit fiddly to convert to DCC.
As I understand it, you need to isolate the motor feed AND return from any connection to the track.
It looks like the one piece pick ups (copper?) actually touch the motor brushes. So, you would possibly need to cut a small section away, or otherwise stop the contact with the brushes.
Then, the pickups would need to be connected to the feed and return wires to a DCC Chip, The Chip motor Feed and return wires would need to be connected to "clips" (Standard Tri-ang "brush clips", as used for the feed wire on X.04 motored Steam Locos.) which fit between the brush and the brush retaining "spring" clip. The "return" side of this spring would require an insulating sleeve, the same as is fitted on the "Positive" side.
(All very "basic", but I don't have any DCC stuff. I have just read a bit!
)
The "Ringfield" motor pickups are different. (But the same "Isolate the Motor from the track" would apply.)
HTH