If you're going to use an APC electric prop you should take a look at the following advisory at http://www.apcprop.com/v/html/tech_support_notice.html as well as the paper insert that comes with the prop. Basically you need to use a tapered reamer and insert it from the front of the prop. Only the bottom of the factory drilled hole is accurately aligned. The tapered reamer will oversize the hole at the top so that the bottom of the hole actually does the alignment. You can find tapered reamers on ebay for a reasonable price.