Here is a little more input on the subject. While you can use a 35 - 40 car or pickup frame for your 41 pickup. There are differences in the earlier frames - it is not exactly an equal swap. I did this on my 41 pickup - I found a good earlier frame mine was of 37 or 38 vintage as it had the frame mount for the cross-steering box. However, this frame did not have the 40/41 style frame transmission mount, provisions for the hydraulic brake master cylinder, no front brake hose tabs, & s slightly different front cross member that had the motor sitting lower. I changed all of these as I had a frame to pull these parts from & I had to make several modifications to be able to mount these parts to retrofit the later parts into my earlier frame. In addition, I had to remove the outboard car body frame mounts (4) 2 per side. So it can be done - but it wasn't a simple bolt in.