well its possible to convert the engine in the rs with the sti tuning and gear but keep in mind the bottom as well as the top ends are not as robust, your looking at converting a sohc open deck with weak pistons to begin with, your looking at a core meltdown....

but fear not it is possible! there are many 2.5rs turbos around, and the key is with its tuning, and yes you will be spending big bucks if you want it to make good power and be reliable and not have to worry about it, trust me you will want to shove that money into reliablilty and not have to cry over not being able to drive you car since the piston melted....

why not consider the older generation gc6\8 bodystyle? its got a much lighter chasis and the cost will be much less which will open up oppurtunities for either a wrx\sti\jdm swap, or a reliable 2.5rs turbo sohc conversion...

and yes they are quick! ;-)