This conversion has been done
many times in the past (in fact, the JDM AE101 Corolla GT came with a 4A-GE 20v Silvertop from factory), and there's a lot of information about it here on the forums, so I'd recommend doing a search. Go to '
Advanced Search', type in a single keyword (such as '4AGE', 'Swap', 'Silvertop' etc) and make sure you click the option in the drop-down box which says 'Search Titles Only'. The engine and transmission mounts are all the same, you just need to change the wiring loom, ECU etc. You can use your standard C50 or C52 gearbox, but I'd recommend using the C56 gearbox as the ratios are matched to the engine and will perform the best.
A member of these forums actually wrote out a very detailed DIY on this particular swap (he used a Blacktop engine, but the process is the same). Here's the link:
AE101/102 20V Blacktop swap info