IMHO for building a period crewcab with an 8' or 8 1/2' bed the best choice would be a hybrid frame using a 157" C30 frame and splicing in a C30 133" rear to maintain the factory top line thus a facory bed installation.
As to reference numbers this is my latest frame specs blurb.
The 67-72 frames are not exactly the same except the K10 LWB and K20.
These are the different PICKUP TRUCK frames as I understand.
Referenced from the GM 1970 truck engineering specifications book.
Any corrections are invited.
SS Tim
C Blazer COIL
C/10 115" COIL
C/10 115" LEAF
C/10 127" COIL
C/10 127" LEAF
C/20 127" COIL
C/20 127" LEAF
C/30 133" LEAF (Longhorn C/20 & C/30, 9' Stepside)
C/30 157" LEAF (Chassis Cab only) included for reference
Note: The 157" frame kicks up a little higher than the 133" going over the axle and does not drop back down like a 133" or 127"
K Blazer
K/10 115"
K/10 / K/20 127"
The frame section and modulus numbers, 39k psi carbon steel through C30s. Note the increased section height, flange width and thickness changes of the frame as the series step up.
C Blazer
C10 115"
C10 127"- 6.04" section height, 2.53" flange width, 0.156" thick, 2.98 section modulus
C20 127"- 6.11" section height, 2.46" flange width, 0.194" thick, 3.71 section modulus
C20/30 133" (Longhorns)- 7.20" section height, 2.77" flange width, 0.194" thick, 5.05 section modulus
C30 157"- 8.18" section height, 2.97" flange width, 0.224" thick, 7.29 section modulus
K Blazer
K10 115"- 6.02" section height, 2.71" flange width, 0.141" thick, 2.70 section modulus
K10 127"
K20 127"- 6.09" section height, 2.75" flange width, 0.186" thick, 3.48 section modulus
http://67-72chevytrucks.com/vboard/s...95&postcount=5
http://67-72chevytrucks.com/vboard/s...2&postcount=12