Well it could be just me however if I have my 2012 FLTRX long enough to require a rebuild that I was not going to do myself, I'd look into one of the "Factory Rebuilds".
Granted I have a 103 and you seem to be dissatisfied with what you have but I can't see taking what I have and putting an S&S motor in it. If down the road I for some reason desire more "punch" than what I've now got (suits me fine) I'd look into bigger jugs, stroking, fuel system, exhaust upgrades or any combination of the above.
Granted I'm new to HD, so maybe there are issues with your current engine I know nothing about. Heck there may be issues with mine I know nothing about yet
A long time ago I realized the formula was very simple and all you had to know was how fast did you want to go and how much money where you willing to spend.
Well I'm 55 years old now and 10 MPH over the speed limit is about all I really wish to do these days and while I have seen the bike do 100 on the speedometer, I'm not really interested in finding out if I can bury that additional 20. That other than fuel really doesn't require much in the way of cash outlay.
I'd rather spend my money on custom paint or other visual effects.