Kit Car Magazine is doing a 40/41 Willys Pickup on an S-10 chassis http://kitcarmag.com/projectbuild/0603kc_hauler/
There are some good photos here that might be usefull.
On the frame slide thing. If you look closely at the frame it appears that the front subframe connects to the side rails in the area even with the front of the transmission pan in the lead photo in the story. it might be possible to cut those welds and slip the frame a few inches to correct wheel base length.
I did much the same thing at the back of a 75 Monte Carlo frame that I put under a 51 Merc.