3 LINK REAR SETUP

Run it up and down a couple of inches each way and check how much the pinion angle changes.

On a four or three link, generally the lower bars locate the rear (front to back each side) and the upper bar (s) handle the load / weight transfer. I doubt if the sheetmetal floor even with the plate you welded on will handle the load over time and you will be pulling your car apart. I would stick to leaf springs unless you are building a race purpose only car....just my opinion, yours may vary.