OK; so what you're saying is that you are at least the THIRD OWNER of this engine... [&o]
Sure; tap out the existing holes and install the new bolts. Maximum expenditure $5.00.
IF that fixs the problem - GREAT!
Go flying.
IF you have any more problems with the little engine - scrap it as a learning experience. [:'(]
You will loose too much time and effort on it. [&o]
Sometimes, it's cheaper to buy a new item.