We did all of the plating with the frame on jack stands.
I didn't take the plating all the way to the transmission crossmember due to the fact that there has to be a way to install the body mounts. If I was to do it over again I would probably do it like my friend did with his '86 442:
He still has to cut his access hole for the body mounts though.
Here's a few pictures I took of my frame along the way:
Passenger side:
Later on I tied in frame side rails to the part of the frame that turns inwards towards the control arm mounts:
Driver's side:
Frame notch:
Something to keep in mind if you do box the frame in, you'll have to bend up your own fuel and brake lines since the stock lines won't fit any longer.