That "huge" hole in the firewall isn't all that big. Some would complain if there was no hole. I don't know about the directions and what they note because when I started this thread there were no directions. However, there have been numerous places in this thread where off-setting the engine has been noted, and in what amounts. I think at one point I even illustrated how to make a drill jig specific for any given engine. Then again, that may have been a thread of it's own.

You need to back up and start the engine mounting process over again, this time taking the time to read through a few of the rather copious notes contained in this thread, and throughout the instructions, and any addendums on the website. Any holes that may aready be drilled in the firewall are easy to fill using a wood dowel of the appropriate size. If you can't find a dowel the correct size, drill the hole out to a size that will fit a given sized dowel. This method has been used for decades to repair holes in props and firewalls and works rather well.

Nobody, but nobody, mounts an engine center line on a firewall centerline. Everyone knows that you offset the engine to compensate for right thrust built into most firewalls. Many even check first to be sure they do or don't have right thrust. Some even use the method noted on the Wild Hare site for centering up the engine. They stand the plane up before mounting the rudder and set the engine inside the cowl on the firewall and make the correct drill locations..... That method has been covered many, many times before, both in the forum and in kit directions.