Ask the "guru"(pres P------T) why one should "not" use a classic for a trainer.
The opportunity for a serious bending of the vital parts on a conventional geared classic airplane's body increased expoentially while being operated as a primary trainer by the "primary student".
GA Horn and many others with long time involvement in flying our old classics are no doubt highly qualified CFIs and very capable of training students in a 170. Even some qualified CFIs have problems. Right Eric? The danger of "bending" increases when the instructor is not in the right seat and the novice pilot encounters a situation that is beyond his/her level of skill. Too many of these classic airplanes have bitten the dust in the last few months to ignore the sudden appearence of MR. MURPHY and his bag of tricks.
I have always felt that the basic training in a craft with a conventional gear adds extra obstacles to a students workload. The intensity of "directional control" management while changing from a flying machine to a driving machine stretches even the ability of many "licensed" pilots. For a student who is learning the many facets of becoming a pilot, the addition of the "sneaky pete" tail dragger's bag of tricks is just begging for problems. I KNOW! I KNOW! "TAIL DRAGGER PILOTS ARE REAL PILOTS!" I have flown with only three or four pilots that I would let fly solo in my "Classic". And they ain't students!

I flew with a new 170 owner from way, way, way, up north who came down here to buy a 170 cabin section (gear box included!) from me. I can fly my '52 from either side so I let him take the left seat. After that flight, I told him as kindly as I could, to go back up there and get with an instructor and get competent in another plane before getting back in the saddle of his "repaired" 170!
(My fwiw,) If you feel it is vital to train a student in a tailwheel airplane, find an instructor who has one to rent or buy a throw-away one like a maule, a citabria, or cub or whatever and then when the student becomes a competent tailwheel pilot, sell the trainer and advance to the 170 of your choice. There is never any guarentee that MURPHY won't jump out of the bushes and grab you but hedge your bet. George stated exatly what my sentiments are - Train them in a C150 or C172 then graduate them to the 170 when and only when they are able demonstrate "conventional gear competency"!