The 2az was the best thing that could happen for us as because of its problems they designed the 2ar not to fail like the AZ did. (Here in Japan many Toyota Noah owners that are holding onto them experience rings, head (soft), sludge and bearing problems.
I know of an AE86 owner that went to great lengths to NA tune a 2az with beautifully designed ITBs, exhaust, cams and valves, porting, rods and pistons only to make less hp than a factory gen 2 3sge. eg. no more than 165hp!!!
On the pic comparisons of both engines posted comparing the factory 2az vs the 2ar inlets you can see how much better the 2ar is for tumble assist where on the older 2az the inlet charge is biased to the opposite side of the cylinder when its forced fuel/air at the top of the inlet valves which coats the exhaust side of the cylinder with fuel.
Living in Japan and surrounded by many owners, gearheads and mechanics they only have disgust for the 2az. I know technology moves along and there is a new engine to replace the AR but like I mentioned many pages ago, the new engine is not designed to be a race motor but an efficient torque unit that operates best at low to mid range whilst the AR is like the last of the big block yesteryear engines (eg Offenhauser) which with development could be the best budget L4 toyota has ever made for enthusiasts.
Another note the AR could be built like the Millington Torque L4 beasts that range from 2-2.8L
Millington Diamond Engines naturally aspirated competition engines diamond series is a purpose built performance engine the Diamond generates a tremendous spread of torque.
www.millingtonengines.co.uk