Yes, it's possible. I used to have two 2500 routers back-to-back with DB60 / V.35 serial cables that I used for testing and experimentation.
Now, you will need to set the serial interface on one of the routers as the DCE by setting a clock rate (I used 64000). Leave the serial interface on the other router as the DTE, and make sure both sides are using the same encapsulation.
Experience is a tough teacher.
The test comes first, the lesson comes later...