I think that it's a great idea, especially if he allows you to share in the work while he "assists"!!! Does he have the capabilities to do machining such as boring?? Does he have a hot tank to clean the block?
At $350.00, even if you had to send out the block for some machining I still think it would be money well spent to have it done right, and allow you to work with him to get the internal knowledge and procedures to make this a one time project!! Geof