Be VERY careful assuming all dark greens, 0 280 150 803 injectors flow exactly the same, I have had a set that were at 80% duty cycle at 300bhp, these had just been cleaned, so of course would be a little lower than old used ones.
Siemens are a direct swap for bosch injectors, but would require a chip change again, I've seen no evidence of a better spray pattern or superior performance over bosch.
I used bosch "greys" 403's on my 200,973 miles old engine and emissions were on mot 0.97% CO, with 137ppm, this was it's 100% normal running mode, not adjusted for mot unlike a load of L6 that may need it, best thing I ever did was aftermarket ecu.
The -31 relates to the spring rate in the actuator itself, this being stiffer/stronger than the std fit one.
As said sounds like a L6, just take cover off and see what the chip says on it, will tell you hopefully what it is MSD are very useful as they keep copies of the chip numbers along with the spec, and the service is very good too from them.
The RS500 coolers are a straight fit but very very tight, they rest on the rear of the headlights but are well worth getting, I use the 70mm airtec one, airtec are very ehavy but very strongly made unlike some of the big name boys whose intercoolers, rads and expansion tanks split the seams due to shit welding.
For 330 bhp you could just use a 4wd intercooler, a T34.48 with 360 bearing will do 380 bhp all day long, used with std cams makes a mentally fast and useable road car.
tabetha