Letter writing format changes little. The content of the letters is what makes them different.
When studying how to prepare great letters and you find one you feel will work for most of your correspondence, stick with that. There is nothing that says you must use fancy formats to get your message conveyed.
Something to remember is that letters are usually written for some type of business purpose. These should follow a business-like format. Of course, when writing to a friend and for reasons other than business, no real formaity is necessary, though many people follow a standard layout.
Letters differ from memos and informal notes. All have their purposes.
Having settled on the type of format that suits your purposes, next consider what is to go into each particular letter. The content is what will dictate any changing.
Letters for business purposes are always type-printed, never hand-written.
In this letters section, we will look at some writing examples of letters to be used in differing situations. Content will be discussed, as will the reasons for writing each one.
The subtle differences in letter usage will be analyzed. That is, the most popular formats include Standard Indented, Block, and Modified Block. I am told each serves a purpose. However, again, I believe which to use is up to the writer of the letter.
On the next page of this section are samples of general letters, letters of recommendation, character reference letters, even formats for questionnaires. These are the main formats of letter writing. You should find a sample there to suit your needs. However, we could be adding more for clarification for various purposes.
In both Volumes of my reference books, Write It Right - Tips for Authors, form letters are discussed pertaining to writing cover letters to agents, editors and publishers with submissions.
Check the samples presented here on site: