460 Dipsticks were located in two places: The front timing cover and the oil pan. I assume your dipstick currently resides in the front timing cover at the front of the engine. When you go to a junk yard, find a motor that has the dipstick in the same location as yours and also has the same pan as your engine. This should be the correct dipstick.

If you are at all uncertain about the dipstick, then all you have to do is change your oil and filter. Add the new quantity of oil per the manufacturer's recommendation, and then dip in the new dipstick and note where the oil level is. Scribe this oil level on your dipstick. If you obviously have a dipstick that is too long (say, six inches dipped into oil beyond the "Full" level that you just marked), then simply trim it down.

Paul