[ted]

The "428" cast in the bottom of the water jacket at the center of the block and and below the center freeze plug is indeed a good indicator of a 428 block but next to impossible to see with an engine in the vehicle even with mirrors and the freeze plug out and the motor mount removed. Even on cleaned blocks, the "428" many times is eroded away by the years of sediment that's settled at that spot.

If not pulling a head, the easiest indicator for identifying if that the motor is a 428 while in the car is to look for the counterweight on the auto trans flywheel. With the TDC on the damper at the six o'clock position, then the counter weight on the flywheel should be visible at the six o'clock position.

The exception to this is that the '66 T-Birds had a two piece flywheel on the 428's that had the ring gear on that flywheel being extra wide (1½ or 2"?) and bolted to the stamped steel flywheel. I don't remember if the '67's had this same flywheel or not but I'm guessing not. The two piece flywheel is definitely a 428 item in the T-Bird but could also make the engine a transplanted 410 from a Mercury. The 410 is unlikely as it would have been put there after the fact but you never can tell. Besides the tell tale two piece flywheel for the auto trans, the wide starter ring will have a visible row of holes at the six o'clock position on the flywheel when the damper is at the twelve o'clock position.

On the other hand, someone could have internally balanced the 428 and used the 390 flywheel which will also throw you. Not likely, but every 428 I've built for myself and many for customers was internally balanced so any zero balanced flywheel could be used without worrying about the balance of the rotating assembly at a later date.

Hope this helps.