429's and 460's are identical down to every nut, bolt and part, with the only exceptions being that the crankshaft and the pistons are engine-specific (but even the connecting rods are the same).
The external appearance is the same unless the original engine tag is still on the engine or maybe the original decal on the air cleaner (not that I would trust this to ID a motor).
One way to identify 429 vs 460 is to flip the motor over and unbutton the pan. One of the crankshaft counterweights (3rd down from the crank snout) has alphanumeric markings stamped on it's edge
, and these markings identify whether it's a 429 or 460 crankshaft.
429 = 4U, 4UA or 4UAB
460 = 2Y, 2YA, 2YAB or 2YABC....or 3Y or 3YA
Also, for quick identification of the crankshaft, you may look for the nodule or embossment between the first main journal and counterweight. The 460 is embossed there, while the 429 is not: