OK I've been doing a bit of searching, and I have read all the various comments about the breathing system on a Supra and come to the conclusion that apart from the actual breathers being a bit on the small side, I can see no reason why I can't treat it just like any other turbocharged engine, and run a vent to air catch tank breather system, I also can't see a reason for blocking off the intakes and using both cam cover breathers, there is a pressure equaliser between the camcover and sump, so no problems there, I read all the bits about the engine not being able to vent without vacuum assistance? and I'm afraid unless there is something vastly different about the Supra engine, I can't see why it should be treated any different from say a Skyline or 200sx motor which hate to be under breathed when power is upped! I also have never had any problems with any engines sucking anything in through the breather system when vented to air! providing that there is a sensible set up, and the pipework is adequate and the vent from the catch tank is long enough and routed properly!
From what I have read about the amount of oil that seems to get sucked into the intake and discharged from dump valves, it certainly sounds like there is a strong vacuum effect from the intake! anyway once I have had my Supra for a while and had a bit of time to investigate further I'll let you know my results.