Were you compensated for the tug operation? if you were, you also need to file a W2-T for Chief Counsel consideration for a special use permit under the National Historic Aircraft Act of 1976 and if granted, they will allow the log time as long as you are using a Skillcraft pen to make the entry. Also, the entry must be completed within 48 hours of the actual tugging or the permit is invalid and you have to apply for a special one time entry authorization which may be witnessed by any CFI with a tailwheel endorsement unless the CFI has been sanctioned in the last there years or anytime since obtaining a student pilots certificate for a designated FAA medical examiner.
It's pretty easy really......