Interested as I've been on all the Rocket forums and groups pretty much for the last 15 years, keenly interested in anything performance mod related. But I've never heard of anyone going with a 3.5 bar reg, certainly not for a stock bike.
I've extensively modified my own bike including the fuel system which was converted to recirc, runs 4 bar pressure reg, 255lph Walbro pump and has 840cc injectors.
Would have to check my detailed files but iirc the stock pump doesn't do much over 3 bar anyway so a higher reg without upgrading the pump mightn't do much.
One can crush down the stock reg slightly anf it'll increase the pressure too if done right.
Anyway. Why did you have to replace the pump and reg?