you won't find any details from the vin/sequence number short of running across some 80 year old with a good memory who worked at the Oakland plant in '58
if those were patent numbers you could search them, the db is on the net - more likely they're casting numbers
with both wheels off the ground they rotate opposite because that's the way differentials work to go around corners, by it locking with one wheel down and able to get traction, it shows it's a posi
1958 was the year GM started a number of rear end options beyond the usual 3.90 and 4.11 [with OD], particularly the 3.38 'mileage minder' ratio, so it's not too surprising you've come up with a rare one, especially on a heavily optioned truck .... OTOH, the 3.92 ratio sounds like what might have been used in the NAPCO conversions, which could have been posi
Bill
