Text Box: This is simply a shortened letter, still having its signature block, that fits into the top half of 8.5 x 11; the full image side graphic uses the bottom half.
Text Box: Here we're back to half a sheet for the "letter" half for the graphic, but note that the signature block has been suppressed and the letter's text is populating the gift card section. This took trial and error to place the text, but since it overprints the graphic, this can work.
In this case, a larger gift card square would have helped, for placement. Also, FYI, the recipient name and $25.00 were added by mail merge, so can be a "variable" section of the letter. 
Text Box: Note three things: (1) graphic appears "shorter." In fact it's using white space to create more room for the text. Signature block is turned off. (2) The green line "Here's… " (ugly usage here!) shows that the letter's text will overprint the graphic.  (3) The bottom captions were added as part of the graphic. This would be a tough placement job using the letter's text editor, not a robust page layout program.
Text Box: Formatting Note!
This product is in layers, with the text editor “on top of” the full graphic, allowing overtyping if desired (3rd sample).
The graphic is the normal 8.76 x 5.75 before bleed, but visual size can be varied by use of white space (2nd sample).

Letters w/ Graphics: Samples