Just as an update:

Having gotten sidetracked onto a different project at the end of yesterday (darn multitasking) I've only now been able to verify the answer:

((((StartingDay - FindDay + 6) Mod 7) + TotalDays) div 7);

Rompel was correct, though in the Pascal implementation the "Div" makes a Trunc unnecessary.

Thanks again to all, I'll feel much better about the way this works now. (The existing solution built up an array in global memory by the slow method. I didn't care for this as it really divorced the computation from the usage as well as requiring an unnecessary global variable).