You should only need to re-shim your fuel head if your system presure is out of spec or if you are running over 400FWHP. Other than that it doesn't matter what the displacement of the engine is.
System presure and warm/cold/boost control presure are different things. Your system presure needs to increase in high HP applications. Low control presure (WUR) will result in a rich condition, high control presure (WUR) will result in a lean condition. When you reset your system presure you must reset your warm/cold control presures (WUR) to compensate for the change. This may be what happened when your fuel head was rebuilt back to stock.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8