My GSM-1 kit came with the bridge post holes drilled 4mm too close together, which I didn't discover until final assembly.

I suggest you have a go with the kit bridge and see if yours is the same. I eventually fixed to my satisfaction at great cost with some offset posts I found and a Kluson bridge (which cost more than the kit did, especially if the first TonePros bridge ). If it's bad, then I'd contact Pit Bull and see if they'd take it back. From your queries about through-body drilling, you probably aren't ready for filling post holes and drilling new ones, plus it spoils the body for anything but a solid paint finish.

There were also smaller issues such as the truss-rod cover being the wrong type and a metal pin at the end of the fretboard pushing the nut out of place. The pin (used for locating the fretboard when gluing it on but put in the wrong place) can be filed down if you remove the nut, and a 3-hole bell truss rod cover is easily sourced on Amazon or eBay (or you can cut down the supplied 2-hole cover and drill your own extra holes).

So worth checking for those issues as well. A shame, as otherwise it was a really good kit.

If you find these issues and are selling it, then you need to highlight them to avoid any comeback on you, despite you being ignorant of them at the time. Which is why getting Pit Bull to take it back if the bridge post holes are out, may be your best option. If you want another kit, they may do a swap.