Most places will recommend against mixing tire types. The difference in construction between the two means they do not react consistently compared against each other in differing conditions. In a panic situation, this mis-match could create a situation where one end of the car behaves differently than the other and the differences between the two, if you are unprepared for it, could cause panic in the driver.
The tracking issue would continue with the rear tires despite the radials in front, even though the front would be more compliant to road irregularities. They also will feel slightly different at speed and will react, and wear, differently. The bias-plys will run hotter and will not tolerate as wide a range of adjustment for alignment purposes. You are old enough you probably remember the "radial tuned suspension" offered on Pontiacs in the late 70s. There was nothing different with it than the earlier suspension, it just had more aggressive alignment specs, which produced a more confident feel for the driver. Compared to a bias ply alignment, radials will allow more caster and camber range before they wear odd. These changes in angle will significantly change the way the car feels to you as the driver.
Have people mixed them, yes. Can it be done, yes. Since you've had your car since new, you likely are very familiar with how it behaves and probably could compensate for the slight difference in feel. Would I recommend it, no.
14" rims....you might be slave to whatever is offered out there that won't be of ideal size. 205/70 up front and 245/60 in the back may be all you can get for them.
Alpha-numeric to metric conversion chart is here:http://www.turbinecar.com/tires.htm
