3737, no vibration to worry about..i helped a mate fit the 1250 kit s/e heads and 42 mikuni carb to a 2005 sporty custom and it went real good i think the mikuni's really help with some power increase!!an 883 to 1200 is worth about 15-20hp ..a 1200-1250 is worth about 3-4hp(all approx)as for mine i've only just run it in definately more torque but i was running out of fuel thru the injectors so i'll give it a good run when i pick it up the dyno guy said they've got heaps more out of it so i'm keen to get it back!!!!