same length as for a 302 or 289. the easiest way to mark one though, if you got an aftermarket stick that is cut to length, is to fill the pan with three qts of oil, then mark the stick at the qt low level, then add the fourth qt of oil and mark the full level. then cut the stick about 1/2" below the qt low mark.
Thank you.
I asked is because I see many different answers. The 71 Mach1 originally came with a 302 and someone sometime replaced with a 351W. The 351 has a 4bbl manifold but the used and adapter to use the 2 bbl orig carb. I have replaced with a 4 bbl now. So I am not sure about the engine other than it is a 3t1W.
They also replaced the dip stick with a chrome handled one. I changed the oil, added a little around, maybe a little more than 4.5 quarts including filter fill. Dip stick shows to the safe mark not the max. Other reason why I was asking.