If you decide to make the changes to Ms. Spalding's curriculum suggested here, you will only need to make a few decisions and implement a few changes to the regular curriculum described in The Writing Road to Reading (WRTR), so that book will be your starting point. This will probably be true even if you use one of the commercial programs.
Frankly, the reason I prefer the Fourth Edition of WRTR is because it's easier to get the meat of the Ms. Spalding's program from it than from the Fifth Edition. The Fifth Edition has a wealth of information for classroom teaching, but a lot of that information should be obvious to a homeschooling parent with some experience.
The Basic WRTR Curriculum
Briefly put, here are the steps that need to be covered:
1. Teach proper posture, how to manage a pencil and paper, and the positions of numbers on a clock, all while instructing how to print the single-letter phonograms.
2. Teach the remainder of the first 50 revised phonograms.
3. Dictate Sections A-G of the Ayres List with your child entering them into the notebook, while beginning to work on writing short sentences and using the words in spoken sentences. Only the Ayres List words go into the notebook.
4. Begin reading books recommended after section A-G words are written in the notebook and learned for spelling. Continue writing sentences using the words, discussing the stories being read, while beginning instruction in the remaining 34 phonograms.
5. Continue through the Ayres List, reviewing spelling regularly, writing daily, reading daily and discussing the books being read.
6. Once your child is older and writing in cursive, switch to a narrower-lined notebook and dictate the seven "rules" pages for entry on the first few pages of the notebook. Pick up dictation of the Ayres List where you feel comfortable and continue with spelling, writing, reading, and discussing the reading on a daily basis.
Never lose sight of the purpose of learning the phonograms and the rules associating them, that is, to become a proficient reader and writer of the English language.
Incorporating the Revisions Suggested Here
The step-by-step instructions on the next few pages cover 1) Decisions you need to make before starting instruction, 2) Modifying WRTR's rules to accommodate the revised phonograms and coding, 3) Teaching the phonograms, 4) Dictating the Ayres List and 5) Modifying the "rules" pages of the notebook. Each topic is covered in detail on the following pages, beginning with Decisions Before Starting.