Keith...
The guy may be confusing the '68 400 H/O engine which had the same YZ code..
If all numbers are original stampings, it looks like your engine could be a '69 R/A III?.
I'm no Poncho expert but using the same old story w/ GM products it's often best to first look at the stampings, skip the castings and count the Vin backwards..
So counting backwards there's your sequential six digits, the seventh digit in is the plant, the eighth digit the vehicle model year and the tenth is the GM Division..
So your eighth digit in being a 9 for a 1969 model w/ a YZ coded block should indicate a Ram Air 111 - 400/366hp w/ Auto trans & 10.75 comp..
By the way, have you tried running the Vin to see if the car is still around?.
~ Pete