just a little bit of RESEARCH turned this up on k20a.org. check out the rating difference between the two.

K20A2
Found in:
2002-2004 Acura RSX Type-S and 2002-2005 Honda Civic Type R (EP, European)
Displacement: 1998 cc
Compression: 11.0:1
Power: 200 hp (147 kW) @ 7400 rpm
Torque: 142 ft·lbf (193 N·m) @ 6000 rpm
Redline: 8200 rpm

K20A3
Found in:
2002-2005 Honda Civic Si
Displacement: 1998 cc
Compression: 9.8:1
Power: 155 hp* (119 kW) @ 6500 rpm
Torque: 139
2002-2006 Acura RSX
Displacement: 1998 cc
Compression: 9.8:1
Power: 155 hp* (119 kW) @ 6500 rpm
Torque: 139 ft·lbf* (191 N·m) @ 4000 rpm
Redline: 6800 rpm
(* Horsepower and torque calculations reflect new SAE J1349 procedures revised August 2004)

45 horsepower is alot to make up and w/ the money spent on pistons,cams,rocker,pins,rocker shafts, you could just get an a2 or z1 and have a motor you haven't touched yet making 200+hp rather then 155hp...

goodluck either way i'm not trying to bash your idea or process of thinking outside the box. if it's your cup of tea to be different so be it, just giving my opinion on where the money could be better spent... free bump