G'day
This it a very good question, most oils that you can get from your local retailer do not meet the requirement for this engine, over the year's oil makeup has changed due to environmental and other issues. One of the issues was the life of the catalytic converter which is greatly reduced when contamination with Phosphorus, oils used to have high level of Phosphorus over 1000ppm, with the introduction of unleaded fuels and catalytic converters the levels have been reduced significantly with some oils having non at all. The prime purpose of Phosphorus is to protect against valve train wear. New technology engines can manage low levels of this, but the old FJ need it. You need to look at an oils API rating. API ratings SC SD SE SF SG are generally Obsolete and have high levels of Phos, current SL and SM oils have very low levels.
I recommend and use PENNZOIL GT PERFORMANCE RACING OIL 25w-50w, this is a proper racing oil that has high Phosphorus levels and all the other good stuff that is no longer in normal oil. It is only available in 1 Qts containers (just under a liter) and come in boxes of 12 and is imported from the USA. You can find it as some Specialist Auto shops at probably around $12+ per Qt, but you can get it directly from the importer in the box of 12 for around $80 to your door.
I don't have their number on me but I will find it and repost if your interested, this is the best grade of oil for these engines if you are using the right bearing clearance of .002"-.003" on your bigends and .003"-.004" on your mains. For the specs of this oil go to the Pennzoil website or the below link.
http://www.pzlqs.com/Tech/Pdsheet/DomesticMarketing/EngineOils/pdf/GTPerformanceRacing.PDF