it _could_ be done but would be a fair amount of work...
As the bigport 4age is farily low compression it wouldnt do you much good anyway.
You would be better off selling the bottom end (for whatever you can get) and dropping in a complete 20v engine. At the moment they are one of the cheapest toyota engines you can buy and are a great little package.
You will need to either find the stock ecu for one or and aftermarket setup.
The current extractors should fit with a little modification to the bolt holes on each end.