the "original" block for my 68 runner is weird also...I have knowledge back to 1970 of the car and motor wasnt ever changed from then on...the block has a mid 66 casting its stamped D383 on the pad no other numbers except but has 2 numbers with an x over them. the julian dating puts it oct 67 assy date and the dates in the bearing inserts are 9 67 my car has a spd of 1 68 so in the assy window, i cant find a vin stamp on it anywhere so who knows, but it had all the correct parts intake exh heads pan etc and all dates are right in line with the engine...is it assy line engine, got me...