I would think a direct call to S&S Cycle would answer all your questions about buying a modified 124 directly from them.
Your 113 would need a new crank, again, to go from 4 3/8" stroke to 4 5/8" stroke. Cases would need to be bored for the 4 1/8" bore cylinders, again.
Why not sell the 113as is, buy a new T124, I'd chose the HC version if I was looking for a good jump in HP.
Despite people claiming the 640 cams need to rev up to make power, they are very on the drivetrain, and with a suitable exhaust and throttle body can usually pull 140hp+. The LC seem to be around 130hp.
My 8 year old T124 crate motor has 70K on it now, no problems, seems to be every bit as fast as it ever was, will run on 87 octane gas when its all that's available, gives good gas mileage. It still uses almost no oil, maybe 1/2 pint in 5K. Mines carbed with an old style Propipe, still delivered 126.5hp/134t in my 01 Dyna. fwiw twinotter