I'm just repeating something I read on a website somewhere, but it was my undertsanding that there are differences in the strength of the bottom end for the two engines. I'm sure you can slap on the turbo, intercooler an such but it's probably cheaper to swap for the 7m-gte than to totally rebuild yours. On the other hand, I'm eventually going to put some boost on my 5m-ge, and see how long it takes to kill it - you could do the same.
On a Mk3 it's probably cheaper and better just too pick up the required electronics to convert from GE to GTE. You need the harness, CPS, AFM, ECU, injectors, and ignitor and change over on top of all the turbo hardware. All this stuff is plug and play in Mk3s. If you plan it out right you could probably upgrade at the same time with the Lexus AFM, 550s, and a 60 trim CT26. The GE engine has higher compression and no oil squirter but these shouldn't be a problem unless you are going after mega hp.