There are a lot of different ways to solve the stipped-bolt receiver portion of your engine.
I would recommend looking into a helicoil. Try this:
http://www.emhart.com/products/helicoil.html
Also do a search on the site using the word: helicoil
The search button is in the upper right corner. There are quite a number of discussions regarding the use of a helicoil.
Jeff