Pretty sure the SP1 swingarm isn't cast iron. It is just extruded aluminum and not hydro formed like the SP2. It is heavier and shorter though. The pivot bolt is also smaller on the SP2, which requires a sleeve not available from Honda unless you buy the cases for an SP2.
Here is a post I did on another forum:
To tell the SP1 (00-01) from an SP2 (02-06) there are many different things besides paint to check.
Here is a breakdown on the paint schemes:
-00-02 are the same paint
The rest are all different paint schemes:
-03 red/silver, black wings are a tad different than the rest of the silver/red bikes, No "Honda" along the bottom, smaller flat black area on the front vs. big number plate on the 00-02, black tail with silver number plate
-04 Nickey edition, black wings match the 00-02, but it has the signature on the tank, came with stickers (some didn't get put on at the dealer), bare frame, silver tail, white numberplates front and rear, says "honda" along the bottom of the side fairings, but it is a little higher up to allow for the stickers
-05 black/grey, doesn't say "racing" under the RVT on the side, little Honda wing logo on the tank is black
-06 black/grey same as 05, but little Honda wing logo on the tank is silver
Differences between SP1 and SP2:
-RADIATORS SP2 radiators have three mount locations, and two fans as apposed to one, SP2 also used the ECU to turn the fans on, SP1 used a thermo sensor in one of the radiators
-OIL COOLER SP2 oil cooler is vertical on the left side, SP1 is horizontal in the center. This means the center "V-cowl" is different.
-REAR FENDERS The SP2 fender is easy to spot as it places the ECU in a vertical box on the right hand side that sticks out below the tail at the front. SP1 fenders have the ECU laying flat.
-SUBFRAMES SP1 has two fairly stright pieces of square alumiunum tubing and some extruded pieces that go up to the top mount, SP2 has some bent square tubing that goes under the seat and to the top mount, then smaller sections going to the rear.
-SWINGARMS SP1 is ugly, SP2 is awesome. Oddly, the '01 was the only year without bungs welded on for stand bobbins
-FRAMES SP1 has a smaller cast front frame spar, SP2 has a stamped larger one, SP2 has gussets inside the frame by bottom of the steering stem, SP2 has holes for the extra radiator mount, and SP2 has a bung welded on the left hand side for a steering damper, SP2 also has a larger diameter steering stem
-WHEELS SP2 has five spokes, SP1 has six
BRAKE ROTORS SP1 front rotors were only 4.5mm thick, SP2 were 5mm thick. Both were 320mm
-FORKS SP2 have a longer top out spring, SP1 have silver preload adjusters on the top, SP2 have larger black preload adjusters that look just like cbr adjusters. The caliper bracket mounting bosses on the SP2 forks are one long tab with two holes, SP1 forks have two separate tabs for each bolt. '05 and '06 also have a lighter gold anodizing finish on them, others have a dark bronze color.
-REAR SHOCK SP1 shocks have the reservoir going up and back like cbr's, SP2 have it going side to side
-ENGINE SP1 have round exhaust ports, SP2 have "D" shaped ports, The right hand side cover (the larger one behind the round clutch cover) is silver on SP1 models and painted gold on SP2 models to match the clutch cover and valve covers. This is the case for US spec, others may be different. The SP2 engine has a sleeve for a smaller swingarm pivot bolt. The sleeve isn't sold through Honda without ordering cases for an SP2.
-EXHAUST HEADERS Different port shapes to match the heads, and different routing of the pipes. SP1 and SP2 exhausts are NOT interchangeable unless they are full systems, but some of those might hit the swingarm if it is incorrect for whatever year the exhaust was designed for, slip ons are not interchangeable unless you swap headers or can cut and weld them. This also means the stock canisters are different and will interchange.
-FRONT FAIRING STAY SP1 had a black steel unit, SP2 is bare aluminum
-THROTTLE BODIES are larger on the SP2. Which means the airboxes and velocity stacks are different.
-FUEL INJECTORS SP2 are 12 hole, SP1 are 2 hole
-ECU's are different due to the injectors and cooling system differences
-WIRING HARNESSES are different for the same reasons as the ECU
-TRIPLE CLAMPS are different due to the steering stem differences, SP2's have a larger stem
Obviously paint and swingarm are a dead giveaway, but those can be swapped. Best way to tell without taking off the fairings is to look at the steering stem nut (much larger for the SP2), the engine cover on the right side behind the clutch cover, or the oil cooler location as these are things that wouldn't/couldn't be swapped.