The block casting # will be behind to passenger side cylinder bank. That will tell you what block it is. The date code will be at the back of the distibuter plateau. (a letter & usually 3 numbers) That will tell when the block was cast. The block code will be on the passengers side front of the block just below the head along with a sequential number of the block. The serial number of the block, which will be a partial of the cars serial number, will be at the lower passengers side front, next to the timing cover, or in some cases, partially covered by same. This is the only number that will tell you for sure if it's the origional engine. The other numbers, with the exception of the sequential # will tell if it is a correct block. The head code can be found over the two center exhaust ports and can be useful, also.
016870 is, as I said, the sequential number of the block. (the 16,870th block cast for the year that it was cast. The YH is the block code. It is definately not the original engine for your car, as the YH was not used in the A body in '68, but if it is a '68 YH block it was a 375 hp. 428 w/four bolt mains. to know what year block it is, get the date code from behind the distributor. By the wayall of the YH blocks were either 421, 428, or 455 until 1974, when they used that code on a 400. Get the date code and the head code and I'll tell you more.
thank you very much, we will get the numbers this week and get back to you. it needs interior and paint, but engine and drivetrain freshly rebuilt and runs great it has hide away headlights and tach on hood and it is a 4 speed would you by any chance know whats its worth?
I can't give you an estimate of its value, but if it has a 4 speed, it was probably built with one and would be worth more. Did you get the numbers that are cast over the center exhaust ports on the heads? That might help me figure out what it could be.
The 62 head was a big valve head used on 1968 350 hp 400s and the 375 & 390 hp 428s in the big cars. That head was also used on the 330 hp 400 in the Firebird. One of the YH engines was the '68 375 hp 428s, so I'll bet that that is what you have, but we won't know for sure until you get that casting date code.