Siamesed bores touch each other side to side, no water passages. Originally thought to make the bores run too hot, now is realized to stabalize the block better due to the extra regidity.
Pump Gas is any gas you can get at a local gas station and pump dirrectly into your tank. 87-89-91-93 are all pump gasses. Different parts of the country get different types of fuels. I can get 100-104 from certain stations in my area, I know California only has 87-89-91 octanes, no higher.