welcome to the garage junior!
what makes you say "
This VIN is correct"??
the first digit should be "J" for a 3/4T conventional cab [not an O listed], and 3406, being the model number, indicates a forward control suburban!
check here , you'll see it doesn't compute
the form of the vin should be
1st digit = weight and length - H[1/2T] or J[3/4]
next 4 = model, 34 is forward control, 06 = burb
the F = assembled in Flint
255= 2nd series 1955
not sure about the XA, it'll be special egine/trans details
where is the number located on the truck?
edit: ahhh! the "vin" is on yer title, not on the truck, that number is an engine number - O340640 is the engine sequence #, F=Flint, 255= 55 2nd, XA=trans/application
Bill