60 speedometer cable

[Clark O.]

I have a 60 serial # 4256 with a build date of 2/25/60. The 58-60 Technical manual page 81 section 30.C states that the speeedometer cable should be encased in a black vinyl casing as they randomly appear after serial # 3000. All I can find is a grey casing and the people at several supply houses think that is correct. Is the black casing actually correct. Another option might be to simply install a spiral steel cased sheathing because my car is probably still in the phase in period. What do ya think?

Thanks
Clark Olsen