I hate to give you a hard time, but you've got a lot of variables going on there, dr.
One would think that a monofilament poly would be pretty consistent, but two 40' sets cut from the same reel can often be a gram apart. Hard to believe, but true.
Head pallets, well +- 2 grams is not unusual for any given pair. I've seen worse.
Synthetic grips are generally more consistent than leather, but not always equal. Overgrips are no different.
If you're using a scale that only reads to the nearest gram, that's another opportunity for inconsistency. Ex, 330.0 and 330.9 can both read 330 on such a scale.
I'm assuming your mods have created equal balance points in addition to weight, but swingweight is another can of worms, and a vitally important one at that.
Pro customizers measure racquets at every step of the build process, starting with the hairpin. The bottom line is you will do yourself a service by measuring the racquets unstrung, before you've installed the pallets so you know exactly what you're dealing with. You can assess all the differences more accurately this way... I feel I should be able to articulate this more clearly and thoroughly but the wife is out of town and there is a long line of empty beer bottles on the kitchen counter as I write this... and I'm running out of steam. Besides, aren't you an engineer after all? You should eat this **** up.
Not withstanding that QC is a b!tch!!!