GT is right, in 55 good odds it was a 272. The 292 was still the BIG motor for the T-bird. You can check John Mummerts site for ID info http://www.ford-y-block.com/technical.htm
If you get the HP rating off the data plate, you might be able to figure it out from the Cylinder Head ID page off that site. 292/272/312 were all the same block, just different bore, stroke, and heads.
thanks for the info..........the car is in Ill. & I'm in Pittsburgh. I'm having a little trouble getting any quick or simple answers from this dealer. But my better-half really likes this wagon so I'm gonna give them some slack for a while..............if no cooo-operashun, I'll start looking elsewhere
If you want to rebuild that motor, you can make a 272 into a 292 or 312. I believe to get to a 292, it's nothing more than a bore. a 312 needs the bore and a different crank. Heads are all interchangeable.