Help modifying window opening. American Concrete Institute standards? Building code?

I’m remodeling my kitchen and part of the work that I want to do involves modifying my window rough openings. Currently, the windows in my kitchen are lower than the countertop backsplash and I want to raise them up above the counter so that they’re easy to open and don’t collect dust and trash, etc.

My house was built in 1968 and it’s constructed of single-wythe CMU walls with no stucco. I’m located in Florida and this construction is very common for older homes in Florida. My plan for this work is as follows:

1. Remove the current wood sills. Lucky me, these should come right out.
2. Mortar an additional row of block into the bottom of the window openings.
3. Secure the new block to the wall by drilling rebar into the sides and through the bottoms of the existing block.
4. Fill the CMU webs with grout.
5. Mortar a new precast sill on top of the new row of block.
6. Install new windows.

I’m doing this work on an owner/builder permit. I submitted this week to add this window/masonry work to my existing permit and my city’s building department has come back to me asking for additional information before they’ll approve. They’ve asked me to show compliance with Florida Building Code and the American Concrete Institute for the alteration to the window opening that I’ve proposed. I’m generally familiar with the Florida Building Code but I am stumped by one requirement – more on this later.

It’s the question about showing compliance with the American Concrete Institute that really has me concerned. This is a lot of information to read, and I bet that the parts that I need to be concerned with comprise only a very small part of their total body of standards.

My first question is, is anyone familiar with the American Concrete Institute’s standards or requirements, or best practices, etc. and can you point me to the general direction of what I should read to learn enough to ensure that my alteration will be compliant?

My second question has to do with the Florida Build Code 6th edition section R703.4 "Flashing." Specifically the requirement that "Approved corrosion resistant flashings shall be installed at the following locations… #3 Under and at the ends of masonry, wood or metal copings and sills." Does this require that I install flashing under (and to the sides of) the precast concrete sill? If this is required, how should I attach the sill to the block? I would expect the use of a sill pan, for example, would prevent adequate surface for mortaring the precast sill to the block. If I can’t mortar the sill to the block, what will hold it in place?

I will be flashing the window according to the window manufacturer’s instructions (Pella), but these of course don’t say anything about the window rough opening or sill construction.

The included drawing should hopefully convey the work that I’m doing. Any help at all as appreciated.