On a serious note, I would think that any bike you modify and almost double the power is always going to be less reliable. I'm not saying that the builder is not good, but their are so many variables, that the builder has no control over, like.....
How the owner of the bike rides,maintains,stores, and how often he uses the bike are all factors in longevity.
My neighbor ruined his HD because he cold starts it and then drops the hammer to redline 30 seconds later. Undoubtedly a dope, but their are a lot of dopes out there.
Now if you modify a bike to add a little power and smooth out some of its design issues, say a mild tune, get rid of the cats and let it breath a little better I'm sure your reliability won't suffer much, if at all.
Now if I were you this is what I would do.
1) leave the Rlll in a mostly stock state for comfort and reliability.
2) drop a Bonneville off at carpenter racing ( or order the parts and do it yourself)and let him have his way with it. The reason I say that is.
A) you can pick up a used late model Bonneville Cheap.
B) replacement, and aftermarket parts are plentiful.
C) it's a lighter and eaiser bike to work on.
D) it will be less expensive to maintain and ride.
E) you will have a very fast retro looking bike and will take everyone by surprise when you blow their doors off.
Of course this might not be what you want and if your over 6'2 you will look a little bit over sized for a Bonneville?
Have fun making a choice and I'm sure it will work out for you. Their is no utopia and everything is a trade off.
Disclaimer: I am not saying that Bob Carpenters modified bikes are not reliable, this is just the logic I have in my own head about any highly modified engine.
Sorry for the long response, I was not busy today!