Derek,
unfortunately, my book ("Military Vehicles in Detail Armoured Halftrack SdKfz 250/1 to 250/12" by Terry J. Gander) mentions the 251's only tangentally.
(they used the same engine, but had different transmissions)
the info on the track is for the 250 series:
38 links 9.5" (240mm) wide, connected by lubricated needle bearings.
has a nice exploded diagram of track pieces.
oddly enough, "The Illustrated Encyclopedia of Military Vehicles" (Ian V. Hogg & John Weeks) makes no mention of EITHER series !
sorry i do not have answer.
and a look at my 250/3 and 251/1 does not make it any clearer.
tracks look different on box art, but the Rommel's "Greif" might not have sported the road treads of the Hanomag.
i will look some more on-line.