Uh, nevermind, I got that first part wrong. It goes with the engine only pre-1970, like you said.
From the Cyborg Cycles site:
Mid 1930's - 1961 engine number is the VIN and is located on left case. no frame number First two numbers are the year Letters (up to four) are the model last numbers are the production number 1962 - 1969 engine number is the VIN and is located on left case. no frame number First two numbers are the year Letters (up to four) are the model last numbers are the production number If production number has four digits, the first number will be even if the year is even, odd if the year is odd If production number has five digits, the first two numbers will be even if the year is even, odd if the year is odd 1970 - 1980:Numbers on both frame and engine. From the factory, the numbers on the frame and engine matched exactly*. (There is an exception to this. See "The 1979 Exception" below). The legal vin number is on the frame. This is a little confusing and is where many people get into trouble. Contrary to what many people think, on any Harley Davidson® made from 1970 up, the title does not go with the engine. You could feasibly have mismatched numbers on the engine, (you can swap engines in your bike just like your car), and as long as the engine numbers have not been altered (read note below) or reported stolen it would be perfectly legal (although it may devalue the bike), But, the number on the title absolutely must match the frame. Example: you have a 1975 Shovelhead engine w/matching title in a custom frame with no numbers. If an educated cop checks the numbers, you are walking home. It will be confiscated on the spot. I know, I know, your ole' buddy Billy Bob has been runnin' a bike like that for years and he ain't never had no problems.......... Well guess what? I've known drug dealers, bike thieves, and prostitutes who have never been busted........sure doesn't mean what they were doin' was legal............Oh yeah, another thing relating to this, I have heard of some states ( Fl., Ca., Mi., etc. ) referred to as "frame states". As if to mean there are "engine states". or maybe "anything goes states" (admittedly, Alabama does come to mind).... No such thing. If you live in the U.S., your 1970 or later title better match your frame. But hey, You don't have to believe me..... When you're standing in the middle of the street, watching your bike swing from side to side on the back of a wrecker on it's way to the Police impound yard, just remember....... I TOLD YOU SO! First two digits are model code Third through seventh numbers are the production numbers (always five numbers over 10000) last two digits are the year code *The 1979 Exception Oddly enough, on some 1979 bikes the engine number did not match the frame number. For only about a month, starting on production date 1/9/79 frame VIN 43000H9 and ending with production date 2/7/79 frame VIN 48199H9, the engine was numbered with a "crankcase number" instead of the VIN. This number did not match the VIN in any way. The example "crankcase number" given to me was ten digits long, and was all numbers with no letters. It did not look like any H.D. number I had ever seen. After "input was received" that the new numbering system would raise suspicion from dealers, insurance agencies, owners, cops, etc., Harley went back to the old system. Obviously, the title numbers must still match the frame.
Many thanks to Bagman for telling me about this, and sending me copies of the dealer service bulletin to verify it. 1981 and later:17 digit vin# number on frame. abbreviated vin# on engine. Title must match the Frame number. Example: title and frame number is 1HD1BDK11BY123456. Engine # would be BDKB123456. All the things I said about 1970 - 1980 frame and engine legality apply here also.