Willy,
The LS Series was made in last half of 1930 and the LT was made in the first half of 1931. I believe these are the exact same trucks built over two model years.
Then later in 1931 they came out with the M Series that were available in 131" or 157" wheel base in either single or dual wheel, I believe this is what you have. All M and N (1932) Series trucks use the same rear axle.
Mike B
