numbers on the frame

[westcoast5]

well I was tinkering around with the truck today and I found these numbers on the outside of the frame on both sides under both doors. Im not sure if its a vin # since when I searched for it, there was posts that it should be on the top of the frame rails by the cab mounts.
The numbers are 2491530 8 26 160 1 under the pass side
and 249159 8 27 160 1 under the driver side. Are these just possibly the frame part numbers? Im asking this since the P.O. was the one who built the frame and he used parts from a 75 or 85 chevy and Im thinking he used the frame too? The cab mounts on the frame have all been cut off and rewelded on but the I250 in there is numbers matching at least from what Im told.
Anyone have a clue?