SStein,
If you are located in the western US the standard 2x6 was still 1-5/8" x 5-1/2 in the early 60's. Therefore, the standard GLB sizes were 5"x9-3/4" (A=48.8 in2, S=79.2 in3), 5-1/4"x9-3/4"(A=51.2 in2, S=83.2 in3) or the same width and 11-3/8" deep. If the dimensions are correct then the GLB was made later from the 1-1/2" thick members and you can just use the area & section modulus for the current GLB properties.
The GLB should have a grade stamp on it but if you can't find it the E value for Douglas Fir in my 1961 edition of the Douglas Fir Use book is 1,760,000 psi. The Fb was probably a minimum of 1800 psi & the Fv (referred to as horizontal shear,H in the book) is 120 psi.
I hope that this helps.