Here is the BT110's on my 393w with highport Vic Jr. copy heads and a big arse lakewood bell housing:
As you can see, ground clearances are excellant.
Clearances are tight between the heads and the shocktower--that is normal and the hard part of fitting headers on a 351w. I did a little hammer work to the shock tower to ensure that all tubes had clearance. Nothing radical, but I wasn't going to modify the headers. Almost had to stand on my head to install the Z-bar but it works great once installed.