Blue print for the lower receiver,
http://www.ar15.com/content/webPDF/lowerBlueprint.pdf


As for the pin channels, if they are in the correct positions, then how loose are the pin channels for the pins.  If just a few thousands of a inch larger than needed, not the end of the world since the pins are supposed to rotate in the lower receiver anyways.  Hence the FCG parts will hold the pins in the lower receiver themselves.

As for is the pins placements and sizes are just slightly off, still not the end of the world, since the FCG itself can be modded to bring the parts back into function.
So on that note, install the FCG parts, do a function test, and if you have problems, than I can walk you through the needed mods on the FCG to get it work correctly in the lower.

And just a FYI, but a drill bit will always drill a channel bigger than the drill bit itself (even when peck drilling), and the top of the channel will be wider than the bottom of the channel.  Hence this is the reason that when you are making the channels for the pins, you start off with a smaller than needed drill bit, then use a reamer to finish reaming the channel to the desired size.