Guys I have googled till my googler broke...i have researched date codes and am convinced that my 289 is the original engine out of my 67 mustang, all of the casting numbers on the heads, block, everything points to this, the only code i am having trouble deciphering is the date code stamped on the deck of the block....here it is: 6L4Z yes a Z not a 2....now whats up with that? Everything i have read said that the code reads as such 6 = 66, L= Nov, then the next 2 numbers are supposed to be the date...now my car was built on Nov 16, 1966....this engine being built on november 4 1966 sounds great, but whats with the Z in the date code? All the sites I read lead me to think that if it was built on the 4th then it should have been 6L04, I dont know...help!