Is this a truck vin???

[jmth52]

I just picked up a block with this info ....
...cast # 3935440
...which is a bbc, 4-bolt main block
...with this vin stamped above the oil filter
...."18B20XXXX"
...could this be a motor that came in a chevy truck
......and would the truck have been built in late August or Sept., 1968 ????
..
....thanks,