maejku-

The backplate gap is not a big issue, unless you really want to use a spinner. I don't.

The firewall has right thrust built into it. IF the cowling is pointed to the left to center the spinner, it is likely that you accidentaly mounted the engine to the left. I am using a Saito .91, and I had to add 3 4-40 washers on top and bottom of the left side of the mount(as sitting in the cockpit) to get it straight while hovering. Before I did this, the cowling lined up very well. Currently I am not using the cowl on it. I think you will be dissapointed with the performance of the .65 in this airplane. You'd be better off with the Enya.