I lowered my 73 620 pretty easy. Just raise the front end off the ground. Adjust the kingpin bolts out. Then you will need to shim the top a-arm and get it aligned. I blocked the rear end 3 inches. Be carfull not to have any material lower than your rim. Otherwise a flat tire can lead to sparks and some bad stuff.
sure, I had my 620 lowered pretty low on 17's. Someone stole it in less than 5 mins from a parking lot. So that's why I got the 63, to fill that gap. Its the grandpa of the 620, hehe. It is truly that easy, a good few hours to do front and back. The front will ride on the bump stops so you can take them off or cut'em alittle.