I'm fairly sure that if it's an Aus delivered 22RE, it has to be the later version. We never got the tall block on anything other than 21Rs. In fact, if it's a 'rona 22RE ('86+ ????) then it has the TCCS EFI rather than analog, which makes it even more similar to the '85+ 22REs in the rest of the world ( we got a weird version in '85 as we were still on leaded petrol - the shortblock engine liek everyone else, but with the older efi that other countries got on their 22REs in '83/'84)
As regards changing the timing chain - the 'proper' way is to remove the head; the bodgy way is leave the head on and drop the sump. When I did this years ago, I did it the body way.
I suggest joining & making a post on the Old Celica email List @ www.celicas.org - they're the 2xR experts