There was a company that made boring bar set ups for automotive engines. I assume this is what you want??
Any way it was simply bolted to the engine block deck and mechanically centered over the bore. This assumes the deck of the block is flat, some thing that might not be true. It has been years since I have seen one. But they would be simple enough to home brew one, one or hunt one up on e bay.. A simple search of e bay for block boring machines might turn one up cheap.. Other wise you will end up buying many of the components anyway. The base and vertical tool post would be fairly easy build, if you have a way to make it nearly perfect. Like dial indicator perfect. If you do not know what a dial indicator is and how to use it, you might be in over your head...
Regards, Kirk