"...under the exhaust manifold..."
go to that side of the car. It'll behind the "down tube" of the exhaust. That's a pipe that comes outta the exh. manifold, (has a donut gasket inside it) that secures the rest of the pipe that goes onto the muffler etc. By behind I mean toward the back of the vehicle.
On the motor is a cast in or stamped on number. It may B hidden by an oil/dirt combo. I hada get some solvent (gas, kero, store bought grease cutter) and a brush to scrub around and find it. Then clean it up to see it. It's worth it to find what is in the vehicle, U never can tell after all these owners & yrs. U don't know the history of all that... The marks will be in capital letter, number, cap ltr, cap ltr. Then 2nd row is mostly all numbers. Both lines grouped together. I think it should say C1XX, meaning (C) 1960, (1) 1961. The Xs = not xs but more ltrs, unknown to me. Let us know what U find sometime (sooner rather than later).
Mine is C8DE & below is 6015-A meaning C - 19(6, 8) - 8, Falcon/Bronco/'stang, etc , E-engine.
The only lrt in the 2nd row I know is A - 170ci motor, I believe.
So for mine - 1968 170 motor in a 1970 vehicle! I had it 27 yrs. & only found out this info when a clutch that matched up w/the vin plate did not fit the motor! I went backwards in my approach to the whole thing... ck out the #s 1st! Even this is not a guarantee but will B alot closer the 1st time.