I've used a lift to replace floor pans and bracin, it certainly does make the job a whole lot easier!!!! Just get everything braced up good, take some measurements before you start and verify they stayed the same before you final weld anything... I also stitch weld the new pans in, and avoid making ant welds more then about 1/2" long... Skip around a bit, use a lot of tack welds.... You'll do fine!!!!