A 3" shackle which is what you need to get the 1.5" of lift will flatten out your main even morethan it already is. A 2" block will be the quickest way to get the lift you want, but as mentioned it will increase axle wrap. For about the same cost as the 2" blocks or the 3" shackles, you can rebuild the current spring pack in about 2-3hrs. Go to your local wrecking yard and grab a set of 53" Chevy springs, or any other fullsize springs that are the same width as the Toyota's, and 2 new spring center pins. This should cost you about $25, the pins run about $2-3, and springs about $20. Take the first leaf down from the Chevy main leaf and install it between the Toyota main and the second leaf. This should give you the amount of lift you need, the leaves just about flatten out w/about 260lbs. You may want to add a second Chevy, or replace a Toy spring with the one from the Chevy. The Chevy springs are thicker than the Toys, so adding a Chevy spring and replacing a Toy w/a Chevy will give you a 1/2" of lift just from the springs themselve. You might have to cut trim the end of the Chevy springs a little, I had to on the last set of springs I did, but not on some of the others I have done.

You should easilly be able to build 2" of lift above the leveling out of the Runner w/o stiffening the ride, just remember to use the longer springs.