SR piston has 19mm pin and 5mm less comp height, to use a 18mm pin piston you also fit a 125mm conrod. Tough engine has steel inserts for the main bearings and a balance shaft to cut down vibes. Original bore plating is crap, if it needs replating you can poke it out to 72mm and run a Gas Gas piston.
Same saggy frontend as E model, add tee and schrader valve run 12psi for trails 15psi for jumps, haven't found the need to revalve mine.
Much heavier bike than E model.
If your wanting to clock up serious k's an XR400 or DRZ400 would be more appropriate, they are similar in weight.