Here's one thread you might look at: page-30 - Post #584
That's the second thread that mentions using IFS hubs and Land Cruiser rotors - seems like Sky Manufacturing Toyota Axle & Differential manufactures/sells the spacers that are required. I don't know enough about the differences and why a spacer is required. You might give Sky a call or send a PM to @darwink1.
BTW, keep your calendar open for this year's Solid Axle Summit in Ouray - details should be coming out shortly from @POTATO LAUNCHER and @CenTXFJ60. It was great running into you on Engineer Pass last year.
The sky spacer allows you to use your existing caliper mounts, if you were to install the ifs hubs without said spacer your rotor would not line up with the caliper. I have read that the caliper can be moved to the other side of the mounting tabs after drilling the threaded holes (in tabs) out to accept a nut and bolt. The sky spacer is a more elegant solution imop but obviously does cost a bit more.
As far as drilling rotors.... i drilled mine only to find out it wasnt necessary after the spacers came in.
Im running an 86 bj60 axle, fj60 rotors, the sky spacer, and 4runner calipers.