thru floor subframe connectors

[the50doctor]

wondering if anyone has any expperience doing these? im trying to put them in, and could use some thoughts. needed to get a convertible in the air to cut out pockets and weld in 2x3 box tube. how do i keep chassis square? dont have a jig. any thoughts appreciated, thanks

[jspeed]

Use ramps/blocks under the tires to get the car in the air and level it off at the rocker panels. Then do all your cutting and welding.