Velobase is a great resource for information. It indicates 112mm is recommended for 68mm shell width. If the track frame has a BB shell of 70mm, then 113mm is the recommendation.
https://www.velobase.com/ViewCompone...d-fde77aff77c8
For the style of riding you are describing, I would think the basic Shimano BB would serve you well, although you might have to compromise and go with 113mm or size down to 110mm assuming there's enough chain stay clearance.