Interesting that 5 days of exposure on pprune and nobody responded--not a big issue, one suspects.
Anyway, tracked down a copy of 2003 FAQ's from FAA on FAR 61, answer found on page 170 (of 471!):"
"Situation 2: A person is undergoing training for an additional helicopter category and class rating at the commercial pilot certification level. The helicopter the person will be receiving training in is a non‑IFR certified Robinson R‑22.
"Question. What are the minimum flight instruments and equipment requirements for this Robinson R‑22 that are used for the instrument training for the add‑on helicopter category and class rating at the commercial pilot certification level that is addressed in § 61.129(c)(3)(i)? Meaning the kind of instrument training where it does not require the filing of an IFR flight plan and flight is going to occur during daytime conditions.
"Answer: Ref. § 61.129(c)(3)(i)and § 91.205(b); The instruments and equipment for the kind of instrument training required for § 61.129(c)(3)(i) during daytime conditions may be as minimal as the instruments requirements of § 91.205(b) with a portable communication receiver, and a portable VOR navigation receiver or some other kind of navigation receiver in the aircraft. As an example, if the training was given in a helicopter, the instrument and equipment requirements may be as a minimum: an airspeed indicator, altimeter, magnetic compass, a portable communication receiver, and a portable navigation receiver."
And the above puzzles even me: how are they going to keep the helicopter right side up if they don't have even a TI/TC for a gyro? Supernatural aid?