Hi Lee -
I've been tinkering with old cars for a long time now and so most of the stuff I know just comes from years of tinkering. What we did to install the subframe was first to weld some square tubing across the frame just in front of the firewall to keep the frame in the same location so when the frame was cut off nothing changed. We took a bunch of measurement from the brace we weld to the axle centerline, end of the frame etc., We even made a jig up that would locate the exact location of the radiator support and the end of the frame so when we welded the ends of the stock frame back to the subframe, the bumper brackets would line up. My brother later decided he liked the look without a front bumper so that saved me some welding. What I did was take the subframe and remove the coil spring and substituted an all thread rod and adjusted the lower control arm so it was parallel to the ground "simulated ride height". I cut the old frame off and slid the subframe under the truck and once the centerline of the subframe was at the centerline measurement I had taken from the original axle, I located the point were the subframe would be cut to mate with the truck frame. My brother didn't want the "in the weeds stance" so I welded the subframe almost even with the top of the truck frame to keep the truck close to stock height......maybe a tad lower. I will admit that we got luck with the V8 engine bolting down on the stock mount location on the subframe. I was planning to make my own brackets to place the motor exactly were I wanted but that wasn't necessary. The 700R4 even cleared the floor and I was even able to take the 79 Camaro tranmission mount and reverse it to make it work.
I wrote a little bit on the subframe swap on my website http://50chevy.freeservers.com/
I am still planning to have those pictures for you on Thursday.