Sorry, the engine sent to you did not have the backplate stuffed. Your engine got a rather plain conversion...venturi, big-bore carb and free-flow muffler. Getting the most out the engine would require to bore the manifold to 5/8" ID like the base of the carb and port the cylinder to match. This could be done but then you would have to get pressure from the case to run the diaphram in the carb to pump fuel. That's relatively easy for me to do...maybe not you???

In order to grind the end of the crankpin it is preferred to remove the shaft out of the engine as the pin is VERY hard steel. The only problem with that is there is a possibility of bending the crank while taking it out unless you are VERY careful and/or use a press. If you grind it while it is still in the case you have to be SURE to seal off the rear bearing so as to not get ANY metal pieces in it. A Dremel tool with a cut-off wheel will work or use a grinding wheel. Either way done with a Dremel will take a while...though it can be done.

In case you haven't gathered...you have to like to tinker with things in order to get all you can out of a conversion...and knowing how to tinker quite well helps!