I would say that you should be able to go 1.5" without having problems with the drag link giving problems by getting too close to the tie rod. I went 1" forward with only about 3.5" of lift and I have plenty of room. I should have gone 1.5" and it would have saved me the trouble of shortening the front driveshaft. I had already made clearance for the tires and torqued the U- bolts so I didn't buy axle relocation plates and go forward more.
I believe that
@Fastereddie went 2" forward when he had leaf springs.