I paid 4k for an s&s 106 kit with forged pistons, cams a 2 into 1 exhaust a new k&n oversize air filter and cover and a dyno tune to get it all running right. The difference was like light and day mate. I'd skip the 103 kit as you will soon get bored of it and go straight to the 106. I'm just waiting for the warmer weather the come back now it's got some Kay's ont the motor so I can get it re dynoed and see what she can really do

From what I read the S&S 106 barrels are stronger. The pistons are forged and give good compression. I think the power you new motor makes will depend highly on the head work and porting matched to your cams and valve size intake manifold size etc. in my opinion the 106 is the way to go as it delivers more torque and makes it easier to ride. Mines got 114.7hp and 120.5tq. Best ET on the 1/4 mile is 11.47 at 115 mph with stock gearing.

thats impressive, yeah your right ya need to make sure ya got the right person doing the build whatever choice ya make