[SkyKing]

As far as obtaining the instrument rating on your airplane, multi-engine land (private or commercial) certificate, instructors are certified as to the class rating, i.e., if you're obtaining the instrument rating in a single-engine airplane, the instructor need only have an airplane category rating with a single-engine class rating. However, for a 337, while designated a 'CLT' airplane in FAA jargon, it nevertheless is a multi-engine airplane, and therefore, to obtain your instrument rating in your 337 you will need a ME rated instrument instructor. Bottom line is that the pilot certificate must be appropriate to the category and class of aircraft in which the instrument training is being provided. See, e.g., FAR 61.195 et seq. As a further requirement, the flight instructor in the ME airplane must have at least 5-hours PIC time in the specific make and model of multi-engine aircraft. You'll find that requirement in FAR 61.195(f).

What you could do, if you have a flight instructor friend with only single-engine proficiency/ratings, is to let him obtain his ME/CLT in your airplane + the 5 hours PIC and then he could instruct in your airplane... maybe you could hornswaggle a trade for time or something.

Good luck!

SkyKing