So I have the head of my engine off now and I would like to solve a riddle and get to know things a bit better in there. This car came to me with a fuel injected head that had the ports plugged, sitting on a B18 block. From what I know the advantages of this are larger valves or maybe hardened valve-seats. A disadvantage might be that the block bores were not bored out and there is a mismatch in diameters. I don't know if the previous owner was just kind of a scrapper and that was the cheapest head he could find at the time, or there was some method to their madness. I'm hoping there is some advantage to this set-up rather than dissadvantage.

How can I find out what's going on here? What are the normal diameters for these components between B20 and B18 blocks and heads? Also, does anybody know some tricks for measuring diameters with regular rulers, as I was a bit shocked at how expensive machinist's calipers and tools are.