can anyone tell me which volvo engine they put in the recent RS, the 300 hp one?

The "same" as in the ST, what exactly are you looking for?

You can find that engine in the volvo s60. Five cylinder turbo engine.

Volvo C30

S40 and V50 if that is what they are asking

Also found in other Ford vehicles

B5254T3

It has VVT and is turbocharged and intercooled. Unlike previous designs, the turbocharger is integral with the exhaust manifold. It uses the Bosch ME 9.0 engine management system. [1]

Using the M66W (FWD) or M66C (AWD) manual transmission output is 230 hp (168 kW) at 5000 rpm with 236 ft·lbf (320 N m) of torque at 1500-4800 rpm. [2] With the AW55-51 automatic transmission, torque is limited in first and second gear. [3]

Applications:
2004.5-2006 Volvo S40 T5
2004.5-2006 Volvo V50 T5
2005 - 2011 Ford Focus ST
2009 - 2011 Ford Focus RS

well i had the idea of swaping my svt 2.0 out with it. any one ever done it?

I saw pictures on FFOC of a guy swapping the ST225 engine into an ST170. I lost the thread and saved pictures, but it had the engine bolted in the bay.