I ran a DUI HEI unit in my SBC short-track car and was flawless. Currently have a stock HEI in my pontiac that I "recurved" myself with lighter weights, springs, and adjustments on the vacuum advance. Since I have a manual trans, I have my total mechanical advance of 36 deg coming in by 2,500 rpm or so, and maxing out around 48 deg with total mechanical & vacuum advance.
If increasing mechanical advance, be sure to check total advance at high vacuum becuase some vacuum advance units will crank it up to pretty high levels. I use a hand held vacuum pump connected to the HEI to easily check total advance while using one hand to hold rpms up, and the other hand running the timing light!
I assume if you order a custom unit from DUI, it should be pretty close, allowing you to set initial timing at idle and go!