The ECU shouldn't be too much of a problem (famous last words)
Kevin has a Dastek Unichip, which for you who have never heard of it, is a piggy back ECU that sits between the main ECU and the engine, and intercepts/modifies values so as to achieve maximum performance whilst the stock ECU still thinks that everything is dandy.
One of the functions of the Unichip is that is can do boost control, and map boost, air/fuel ratio and timing on a per-rpm and per-throttle load basis. The newer ones can also increase the rev limiter and other nice things too.
The Unichip should therefore be able to take care of running the SR20DET without the stock ECU freaking out, although it is probably going to take quite a while to set up the mappings etc for the DET - just something to be wary of if the performance guys you use charge by the hour for Unichip setups (some charge by the hour, some charge a set amount).
The DET install itself, especially the more complicated GTi-R install, is a little over my head I'm afraid. If you do decide to go ahead, I think that George's pal is gonna be the best person to speak to.
Oh, and I can't really see the point of installing a CA18DET in preference to a SR20DET - not only is it an older technology engine, but it doesn't have THAT much power stock (around 160bhp I think) and I'm certain you'd have to replace your ECU and wiring harness as it is a different series engine.