There is an option for this in TT 120 from Lincoln locos.
https://lincoln-loco.co.uk/class-55-deltic/
I think the Hornby class 50 will be ok depending on how long the actual block is, the class 50 does not have nose ends like the the 55 but the length and bogies are the same, if you can get away with using the Hornby class 50 chassis then you would need to do a battery box to clip on the chassis