Just guessing here, but 72 footers are still "shorties", so at 26" radius I think you'll be OK. You could try two and see how they behave. With passenger cars things like weight, coupler height, and knuckle size get lots more important as the length of the cars magnifies the effects of misalignments. Walthers recommends a 24" minimum radius for their 85 ft. cars. I use traditional #5 Kadees on my passenger equipment, as nobody really sees the couplers under the diaphragms anyway, and I find I have to tune the train to the layout. Talgo couplers are OK for pulling, but terrible at backing the train. The quality of your trackwork and minimum turnout size are also going to be factors. I changed the couplers on IHC passenger cars from talgo to body mount back in the day. These were true 85 ft. cars on 30" radii, and they worked fine.