I have to admit, I don't remember whether the HZJ73 has 55" or 58" track width. But I do remember that the J80 has 62.2" and 63" axle width depending on year. It is a significant width difference so be mindful of other issues that might arise like fender flares, might have to trim the fenders etc. Unless you have some specific issue needing wider track width, I'd suggest just doing a coil swap with the original axles. I have some drawings of the 4Link I designed for my HZJ73 somewhere and for a coil swap in the front, I'd suggest contacting some OME suspension dealer that actually knows what they are doing and also get trailing arms from a J80 (since they are quite easier to fabricate mounts for than the J70 Prado trailing arms which need a machined "spacer".
If you have any more questions, feel free to pick my brain about it on this thread. I've done quite a lot of work on Toyotas and matching different parts together and building my own stuff for slightly modified trucks to heavily modified trucks like my 46" 4Runner, and my 42" HZJ73...